dendrosoma radians, ehrenberg. · on the systematic position of trichophrya, lermno-phrya, and...

DENDR0S01IA RAD CANS, EHRENBERG. 141

Dendrosoma Radians, Ehrenberg.

BySydney T. Hickscm, D.Sc, P.R.S.,

Beyer Professor of Zoology in the University of Manchester,and

J. T. Watlsworlh.

With Plate 10.

CONTENTS.

PAGEP r e v i o u s O b s e r v a t i o n s . . . . 1 4 1O n c l o s e l y r e l a t e d G e n e r a . . . . 1 4 3M a t e r i a l . . . . . . 1 4 5T o o d . . . . . . 1 4 9S t r u c t u r e o f t h e C y t o p l a s m . . . . 1 5 1T h e M e g a n u c l e u s . . . . . 1 5 2T h e M i c r o n u c l e i . . . . . 1 5 7T h e G - e m n m l s e . . . . . 1 6 1T h e F r e e - s w i m m i n g G e m u i u l a j a n d t h e i r D e v e l o p m e n t . 1 6 4O n U r n u l a e p i s t y l i d i s . . . . 1 7 0O n t h e S y s t e m a t i c P o s i t i o n o f T r i c h o p h r y a , L e r m n o -

p h r y a , a n d D e n d r o s o m a . . . 1 7 4S u m m a r y o f R e s u l t s . . . . 1 7 8L i t e r a t u r e . . . . . 1 7 8D e s c r i p t i o n o f t h e P l a t e s . . . . 1 8 0

Dendrosoma radians was first described by Ehrenbergin 1837 (9), but the figures he drew to illustrate its structurewere not published until 1862 (11). In 1840 (10) he gavethe following diagnosis of the species "Dendrosomaradians: D. corpu.sculis conicis, crassis, mollibus lasvi-busque, alterne ramosis, rame apice incrassatis et tenta-culatis £",'"

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142 SYDNEY J. HICKSON AND J. T. WADS WORTH.

Ehrenberg apparently saw the meganucleus, but in hisfirst paper expressed the opinion that it was the male genitalgland. In the figure (11, Plate III A) which he publishedlater he represents a long axial vacuole, probabty the mega-nucleus, and in the description of it apparently abandons theview that this structure is a genital gland.

Claparede and Lachmann (5) gave a good figure of Dendro-soma in 1861, but made a grave error in describing-the mega-nucleus as an elongated contractile vacuole. There is noreason whatever for believing that there is in Dendrosomaany system of elongated canals in communication with theordinary spherical contractile vacuoles.

The next important contribution to our knowledge ofDendrosoma is that of Levick (23), who in 1880 describedand gave a good figure of the gemmule. Levick also gave adescription of the interesting streaming movements of theprotoplasm, which we have confirmed. There can be littledoubt, however, that the "germ and sperm elements" of thisauthor were not correctly interpreted. Notwithstanding thestatement that he actually saw living spermatozoa comparableto those of Hydra discharged from the Dendrosoma, it is, in thelight of our knowledge of the reproductive processes of otherAcinetai-ia, impossible to accept the view that Dendrosomapossesses at any time definite male and female sexualglands.

In 1881 Saville Kent (19) published a more elaborateaccount of the species and gave a figure of a large specimenone tenth of an inch in height, which has been copied withsome modifications in nearly all the text-books of zoology.

The principal new point of interest in Kent's account ofthe species is the description of " certain exogenously pro-duced buds similar to tiiose of Ac ine t a mys tac ina des-cribed by Stein." If Kent's interpretation of these bodieswere correct Dendrosoma would present the very remarkablepeculiarity of producing two different kinds of gemmulaaat the same time. Subsequent authors have referred tothese bodies with caution: Biitschli (2) calls them "angebliche

DENDROSOMA KADIAXS, EHEENBERtt. 143

freie iiussere Knospen" ; Lankester (21), in his description ofthe figure, refers to them as "more minute reproductive (?)bodies."

There can be no doubt, howeve:*, that these bodies are not" b u d s " at all, but epizoic Acinetaria belonging to thegenus U r n u l a .

The meganucleus was described by Kent as follows : " Endo-plast ribbon-like, ramifying and much contorted in thestolon aud basal portions of the main stem, continued as asimple band into the distal region and secondary branchlets."

He gives a figure of the meganucleus in a small portion, ofthe basal part of an arm, which is probably correct so far asit goes, but in the figure of a distal portion of an arm thenucleus is shown to extend much nearer to the extremitythan we have found it in any of our preparations. In. thefigure of the whole specimeu the meganucleus is not shownat all. This figure has been copied by the writers of manytext-books, and in some, as, for example, those of Calkins(3) and Lang (20), the meganucleus has been added to thefigure and erroneously shown to extend to the extremity ofall the branches.

The other genera of Acinetaria that are apparently closelyrelated to Dendrosoma are T r i c h o p h r y a (C. and L.), L e r -m e o p h r y a (Perez), A s t r o p h r y a (Awerinzew), and D e n -d r o s o m i d e s (Collin). Concerning A s t r o p h r y a we haveat present only a short note and figure by Awerinzew (1).The single specimen obtained was found free in the planktonof the Volga, aud, like some of our specimens of Dendrosoma,it had a massive test of adherent sand grains and plantdetritus. As it is figured with long arms and rather shorttentacles its affinities are apparently with Dendrosoma ratherthan with L e r n s e o p h r y a .

The genus T r i c h o p h r y a seems also to be closely allied toDeudrosoma. I t is found on the stalk of Bpistylis and onthe appendages of Astacus and various Entomostraca. Wehave found specimens which we attribute to the genusT r i c h o p h r y a in our material obtained from the Bridge-

1 4 4 SYDNEY ,T. HICKSON AND J. T. WADSWORTH.

water canal. The genus may be distinguished from Dendro-soma by its small size, by the shortness and unbranchedcharacter of the processes that bear the suckers and byother characters which are described later (p. 174) (fig. 46).

The genus Lernaaophrya was found by Perez (25)attached to Cordylophora in the docks at Bordeaux. Wehave also found it associated with Cordylophora in thematerial from the Bridgewater canal. It varies in size, butis usually larger than Trichophrya. It has short, un-branched arms and remarkably long suckers (6g. 48). Inother respects also it appears to be distinct from Dendrosomaand other genera (see p. 176).

The genus Dendrosomides of Collin (17) was found onthe thoracic appendages of Eupagurus cuanensis. Itappears to have some affinities with Dendrosoma,, but on thewhole it seems to be more closely related to the Ophryo-dendrinse.

The genus Staurophrya,1 Zacharias, is a free fresh-water form, with short arms, long non-capitate tentacles.Its affinities are obscure.

There is very little information at present as to thegeographical distribution of Dendrosoma. All that can besaid is that it has been found in Europe and in the UnitedStates of America. According to Ehrenberg it is found onCeratophyHum, Callitriche, and on dead leaves. Kentfound it on Anacharis, Myriophyllu m, and other aquaticplants. Leidy (22) states that it is found in America onCeratophyllum, and attached to the rotifer Limniassocialis. Stein (27) briefly refers to a species, Dendro-soma astaci, attached to the appendages of the fresh-watercrayfish. As suggested by Kent it is very probable that thisis the same species as D. radians.

1 The only account of this genus we have found is in Deluge's andHerouard's ' Proto/.oaires,' p. 514.

DENDJROSOMA BADIANS, KHBKNBEBC. 145

MATERIAL.

The first 'material we examined was supplied to us someyears ago by Mr. Bolton, of Birmingham. Since that timehe has forwarded to us living specimens on several occasions.The Birmingham material is usually attached to waterplants.

A few years ago the Rev. T. Robinson, of Hale, informedus that Dendrosoma could be obtained in the Bridgewatercanal, in the neighbourhood of Altrincham, attached tospecimens of Cordylophora, and we have found it thereand obtained an abundant supply at all times of the year.For rnauy months it is principally attached to the hydrocauliof living Cordylophora, but we have also found it on thestalks of freshwater Polyzoa and on weeds. In the winterwe have found specimens on the perisarc of the hydrocauli ofCordylophoras that have died down. It is noteworthy that wefound these specimens a few days after the severe frost of Decem-ber 25th to 30th, 1908. They were very plentiful, healthy,and were giving rise to a great many geminulas. They werealso provided with a considerable number of epizoic Urnulas.These facts seem' to prove that there is no special advantagegained by the Dendrosoma in being associated with theCordylophora other than that of position. It seems probablealso that Cordylophora gains no advantage by the presenceof Dendrosoma on its hydrocauli.

A difficulty in the investigation of the Dendrosoma foundin the Bridgewater canal is, that the test becomes encrustedwith a thick coat of what we can only call black dirt (text-figs. A and B). This renders the observation of the structureof the stolon and the proximal regions of the arms in anythingbut sections extremely difficult. The material obtained fromBirmingham is much cleaner. Associated with the Cordylo-phora and Dendrosoma in the Bridgewater Canal there areseveral other genera of Acinetaria, Vor t i c e l l a , Car-chesium, E p i s t y l i s , and S t e n t o r , besides worms,Rotifers et hoc genus oinne.

146 SYDNEY J. HICKSON AND J. T. WADS WORTH.

Of the other genera of these Aciuetaria, two are of con-siderable importance in relation to Dendrosoma. These arethe genera T r i c h o p h r y a (Clap, and Lach.) and Lernfeo-p h r y a (Perez).

At one period in our investigations we were inclined tobelieve that both these genera represent young phases in thelife-history of, or varieties of, Dendrosoma rad ians , butwehave since arrived at the definite conclusion that they arecertainly distinct species. The relation between the threeforms will be discussed later on, but we may state here thatwe are in agreement with Perez in considering LernEeo-p h r y a an intermediate form connecting Tr ic l iophrya withDeudrosoma and justifying the inclusion of the three generain the distinct family the Dendrosomina (Biitschli). It is amatter of considerable interest that the three closely alliedgenera should be found associated together in this mauner inthe same locality. The struggle for existence between thedifferent Acinetaria and Ciliata must be very keen, and it issui'prising that the thi'ee genera should have survived side byside. In the material from Birmingham we found no .examplesof either T r i c h o p h r y a or Le ru t eophrya .

The specimens from the Bridgewater canal consist of anirregular base or stolon attached to the perisarc of the hostfrom which a number of free branches or " arms " project atvarious angles into the water (text-tig. A). It is difficult toform any very definite conception as to the size to which asingle individual may attain, as the stolon is usually so thicklyencrusted with dirt of various descriptions, and bends sofrequently from one side of the Cordylophora to the other inits sinuous course, that the limits of the individual are oftenimpossible to determine. We have measured single un-branched arms of this form that are '5 mm. in length (text-fig. B). The tentacles are very extensile, and may be 75-90 ix in length. The arms arise from the stolon at irregularintervals, sometimes in clusters of three or four, sometimes atintervals of one or two millimetres. There appears to be nogeometric law governing the origin of the arms ; but an arm

DENDBOSOMA RADIANS, EHRENBBRG. 147

seems to be pushed out wherever an opportunity occurs forone to reach a food supply.

TEXT-PIG. A.

A specimen of Dendrosoina rad ians , attached to Cordylo-phora, from the Bridgewater canal, near Manchester, c.v.Contractile vacuoles. gem. The "internal buds" or gemmulse,'me. the long strap-shaped meganucleus, me', the meganucleusin the base of attachment, showing at me", an irregular dis-tribution of its chromatin granules in the cytoplasm; t. thetest covered with dirt and foreign particles of various kinds.v. The so-called " external buds," now shown to be a speciesof Urnula , are seen at the extremity of some of the branches.The figure is senii-diagramniatic. The outline was drawn withthe camera lucida from a very large, branched, living specimen,and the structural details filled in.

The specimens from Birmingham diHer in some respectsfrom those found in the Bridgewater canal. The former

148 SVDNJiY J . JBICKSON AND J. T. WADSWOBTH.

attain to a greater size, their arms are longer and branchmore frequently, and they seem to possess more micronuclei.It is difficult to express the differences between them in exactterms. Some specimens from Birmingham are very similarto some specimens from the Bridgewater canal, and there is

TEXT-FIG. B.

This figure represents the more usual form in which, the varietyof Dendrosoma radians from the Bridgewater canal isfound. It is attached to the hydrocaulus of a Cordylo-pliora. The longest of the three arms was 0'5 mm. in lengthand unbranched. The longest suckers are 75-90^ in length,c. Cordylophora hydrocaulus. c.v. Contractile vacuole.

undoubtedly a great range of possible variation in specimensfrom both localities. The specimens from Birmingham areundoubtedly more closely related to the original type speci-mens of Bhrenberg and to those described by Kent than are

DENDROSOMA 1UDIASTS, EHBENBEEG. 149

the specimens from the Bridgewater canal, and we have nohesitation in naming them D e n d r o s o m a r a d i a n s Ehren-berg. I t is a matter of opinion whether the specimens fromthe Bridgewater canal are sufficiently distinct to justify theconstitution of a new species. After careful considerationwe have come to the conclusion that they are not. All theprincipal differences, except that of the number of the micro-nuclei, may very probably be due to the direct influence ofthe environment.

FOOD.

For some time we were unable to record any observationson the food of Dendrosoma, the animal appearing' to bevery refractory in this respect as compared with D e n d r o c o -rnetes.

We have frequently observed small Ciliata and Flagellataswimming freely among the suckers, and even bumping upagainst them, without harm to themselves or producing anyreaction in the suckers. In September of last year, however,we obtained in the plankton of some ponds near Manchester

.specimens of Bup lo te s and of a green Paramec inmb u r s a r i a ; and, on passing some of these under the cover-slip of a prepai-ation of living Dendrosoma-, several werecaught and held fast by the suckers, and the pi-ocess offeeding began. The astonishing feature of the phenomenonis that Dendrosoma seems to prefer such large prey. AJBuplotes 100/u in length will be held and devoured by aDendrosoma arm that is not more than 15,u in diameter(fig. 30).

When au Infusorian is captured by a Dendrosoma it is notparalysed, but continues to lash its cilia with as great, oreven greater, activity than before.. It is almost painful towatch a Eup lo te s struggling to escape its doom. It willmake a violent effort to move forward and then fall backexhausted for a few seconds, .or it will endeavour to spin

150 SYDNEY J. HICKSON AND J. T. WADSWORTH.

round on its axis. But all the time particles of its protoplasmcan be seen streaming down the suckers of the Dendiosomainto the arm. The Dendrosoma never seems to use the wholebunch of suckers at the end of an arm for feeding at thesame time. From one to six or seven, according to the sizeand strength of the prey, may be used, the others beingstretched out unconcerned with what is going on in theirneighbourhood as if in search of other victims (fig. 30).

The usual statement made in the text-books is that theAcinetaria paralyse their prey before feeding on them, andthis is used as an argument that a fluid of some kind passesdown the tentacle towards the food before the return currentof the food substance sets in. We are quite certain that inDendrocometes such a paralysis of the food animals does takeplace. We have seen on several occasions small Parameciacaught and paralysed by the arms of this remarkable form.Biitschli (2) gives several examples of the paralysing pro-perties of the Acinetarian suckers, and quotes cases observedby Stein in Metac ine ta , Maupas in Sph aerophry a, Platein Hypo com a.

Claparede and Lachmann (vol. ii, p. 50), however, recordthat a Stylonychia caught by "an Acinetau " struggled for along time and then underwent fission. One of the daughterindividuals escaped from the Acinetau, leaving her sister tobe devoured.

Levick (23) also does not mention that the Infusoria uponwhich Deudrosoma feeds are paralysed, but says that thetentacles are capable of "resisting the struggles of thecaptive."

Since we made our first observations on the feeding ofDendrosoma we have occasionally found a smaller int'usoriaucaught by the tentacles, but time after time we have failedto induce them to feed upon the common P a r a m e c i u maure l i a from our cultures.

But although we have succeeded in inducing the Dendro-soma to feed we have failed to keep them alive in the labora-tory for more than a few days. The material soon becomes

DENDBOSOMA BADIANS, EHRENBERG. 151

putrid owing to the death of the Cordylophora and the decayof the roots to which it is attached, and we have not succeededso far in getting the specimens to become fixed to any othersupport.

THE STRUCTURE OF DENOROSOMA.

We have very little to add to the knowledge of the suckersand the general cytoplasm of Dendrosoma. The suckers areof considerable length, terminating in a small knob or cup.Tliey are usually quite rigid when extended, like the suckersof most of the other Acinetaria, and they can be slowlyshortened when circumstances become unfavourable. Beingvery slender and transparent we have not been able todemonstrate the presence of a definite lumen, nor have weseen even in the shortest suckers any evidence of a spiralridge such as can be seen on the retracted suckers of some otherAcinetaria (fig. 45). In several of our series of sections wehave been able to trace very delicate lines running downsome distance into the arm from the bases of the suckers.

The cytoplasm is usually clear and transparent. In tlieliving arm a streaming movement of minute granules can beclear-ly seen, as originally described by Levick. In well-stained preparations the cytoplasm appears to consist of adelicate network of fibrils enclosing a number of minutegranules which staiu faintly with acid dyes, but there arevery few elements in the cytoplasm that give a deep stain withbasic dyes. We have found no evidence in our preparationsof bodies corresponding to the "Tinctinkorper" of otherAcinetaria in the arms or stolon where the meganucleus isclearly delimited. In some cases, however, when the mega-nucleus is scattered (see p. 156) the cytoplasm is filled withnumerous chromatin bodies which may be derived from themeganucleus.

Martin (24) suggests in a recent paper that the " Tinctin-korper " of other Acinetaria represent in some cases thechromatin of the nucleus of ingested prey. ' The difficulty we

152 SYDNEY J. H1CKS0N AND J. T. "WADSWOETH.

have found in getting Dendrosonia, to feed may to someextent account for the absence of Tinctinkorper.

The contractile vacuoles occur at irregular intervals on thearms and may also occur in the stolons, but they are not easilyseen except in those parts which are relatively free from theencrusting dirt (text-fig. A, cv.). The description of thesestructures given by Levick and Kent is correct; the elongatedcontractile vacuole figured by Claparede and Lachmann isobviously incorrect.

THE MEGANUCLEUS.

In a stained preparation of Dendrosoma the meganucleususually appears as a dark band running along the axis of thearms and stolon. It is rarely exactly in the centre, butusually bends first to one side and then to the other, or runs acourse for the whole length of au arm somewhat to one side ofthe exact axial line. In the younger parts of a stolon it hasvery much the same appearauceas it has in au arm, but in theolder parts it is frequently contorted, sometimes broken or dis-continuous, branched, Or knoblbed, and not infrequentlydissipated (figs. 11, 12, 1'3, and text-fig. A).

There is so much variation, however, in the generalcharacter of the meganucleus that it is impossible to describeit adequately in a single sentence.

Although it is usually found to some extent in every arm itnever extends to the distal extremity as it is drawn in thefigures given by Lang and Calkins, and in the younger andshorter branches there may be no part of the meganucleus atall (text-fig. A). We have observed a difference, whichappears to be constant in this respect, between the specimensfrom the Bridgewater canal and those from Birmingham.In the former the meganucleus extends ouly a short distanceinto the arms, in the latter it extends very much further ; butin this respect, as in others, the meganucleus is subject toconsiderable variation. In many specimens the limits of themeganucleus are very clearly defined, in others the boundary

DENDEOSOMA RADIANS, EHRISKBERO. 153

lines are ill-defined and the difference between the mega-nucleus proper and scattered chromidia impossible to dis-tinguish (figs. 12, 13, 14).

If the form and distribution of the meganucleus of Dendro-soma are remarkable, still more so is its minute structure.The difference between the meganucleus of Dendrocometesand that of Dendrosoma in this respect is very striking, andthe first cause we had to doubt the current view that the so-called " external buds " (Urnula) are really produced by theDendrosoma was the difference we observed in histologicaldetail between the meganucleus of these bodies and themegauucleus of the Dendrosoma.

We described in a former paper (16) the meganucleus ofDendrocometes as consisting of " a distinct meshwork ofdarkly staining lines which appears to support a seriesof minute, rounded, chromatin granules." " In the meshesof the darkly staining chromatin there is a homogeneous sub-stance which stains faintly yellow with brazilin."

In the meganucleus of Dendrosoma we have found no traceof a true limiting membrane or of a meshwork. It consistssimply of a number of chromatin granules floating indepen-dently in a fluid matrix (fig. 52). • In this respect, therefore,the structure of the meganucleus appears to be very ex-ceptional.

We have not arrived at these conclusions without verycareful study and numerous experiments. We expected tofind some kind of network, whether of plastin or of chro-matin, such as we found in Den d r o c o m e t e s , Urn ula, andsome other Acinetaria, but the various methods we have em-ployed have given us no positive results. Staining withhsematoxylin and congo-red we have obtained very sharpdifferentiation of the histological structures, and in somesections we have seen a thin line bounding the meganucleuswhich might well be mistaken for a membrana limitans, butafter prolonged research we are convinced that this line doesnot repi'esent a continuous membrane, and that it belongs, notto the nucleus, but to the surrounding cytoplasm. Whether

'154 SYDNEY J. HICKSON AND J. X. WADSWORTH.

our interpretation of this line is correct or not, the factremains that there is a very marked difference between themeganucleus of Dendrosoma and that of other Acinetariaexcept L e m t e o p h r y a we have examined in this respect.

In referring to the meganucleusof A c i n e t a pap i l l i f e r a ,Martin (24) writes : " Generally in whole stained preparationsnumerous spherical dark areas are to be seen resembling theso-called " Binnen-korper" of the Infusoria. In section,these structures, as in the case of some Infusoria and Dendro-cometes, are found to consist merely of local thickenings inthe mesh of the nuclear network, and therefore resemblekaryosomes rather than true nucleoli."

In Le rnseophrya , so far as our observations go, themeganucleus resembles that of Dendrosoma.

In A c i n e t a t r i p h a r e t r a t a , according to Entz (13), thesubstance of the meganucleus appears to resemble that ofDendrosoma and contains a number of sharply defined bodies,but there is a distinct nuclear membrane.

Collin (7) describes the meganucleus of Ephe lo t a gemmi-para as consisting of "grains chromatiques de forme varieesur un substance achromatique," but he finds also a distinctisolable nuclear membrane.

In the iron-brazilin preparations a faint yellow colour canbe seen in the thicker sections between the granules, and iniron-haematoxylin and congo-red preparations a faint pinkcolour maybe seen in the same place, indicating perhaps thatthe matrix in which the chromatin granules float is to someextent capable of taking a faint oxychromatic stain, but nostructure is seen in it even with the highest powers (Zeiss2 mm.) of the microscope we have used in the best light.

There can be little doubt that the granules are rnainlycomposed of chromatin. They give the characteristic stainswith iron-hfematoxyliu, iron-brazilin, safranin, and thionin.They are usually spherical in shape, but occasionally irregular-shaped granules and large lumps (fig. 51) are found in thecourse of the baud.

The variability in size may be seen by a comparison of figs.

DENDROSOMA BADIANS, EHBENBEKG. 155

50, 51, 52, which are drawn to the same scale. Fig. 50represents the terminal extremity of the rnegannolens in anarm, and the granules are of an average size. The diameterof the meganucleus in this specimen was 2 n, and the largestgranules were approximately 0'85 /.i in diameter. Fig. 51represents a longitudinal section near the base of an arm inwhich there were two meganuclear bands nearly parallel witheach other. The larger of these bauds was about 3"4 /j. indiameter. The granules in these bands are extremely small,but at intervals large lumps of chromatiu, in some cases over4 fi in length, occur. Fig. 52 represents a section through aremarkably swollen part of a meganuclens (25'5/uby 20'4/u), inwhich many of the granules are very large; the largest areabout 2'5 n in diameter. The study of the variation in sizeand form of the granules in the meganucleus suggests a com-parison with the descriptions given of the meganuclens inC a r c h e s i u m and other Ciliate Infusoria. In C a r c h e s i u m ,according to Mrs. Bidder (Greenwood, 14), there is a nuclearmembrane which in certain stages is " demonstrable withdifficulty"; the contents consist of granules of two kindsfloating freely in the nucleochyme, and there is no indicationof permanent linin threads connecting these granules together.The granules are of two kinds—the proto-macrosomes andthe proto-microsomes, and of these the proto-macrosomescertainly and the proto-microsomes probably undergochanges in association with nutrition. The larger granulesof the meganucleus of Dendrosoma seem to agree with themacrosotnes of C a r c h e s i u m , although we have not observedthe vacuolated condition which the latter sometimes exhibit.A distinction between macrosomes and microsomes has notbeen demonstrated in Dendrosoma, but it is possible thatfurther investigation might yield similar results to thoseobtained in O a r c h e s i u m . This comparison suggests thatthe great difference we have recorded in the size of thegranules of the meganucleus may be in some Avay associatedwith nutrition.

D i v i s i o n of t h e m e g a n u c l e u s . — T h e only method of

156 SYDNEY" ,T. HICKSOKT AND ,T. T. WADSWOBTH.

division we have been able to follow is the formation ofthe meganucleus or meganuclei oE the gemmulse. Beforethe outline of a young gemmula is seen in the cytoplasm, oneor more kaob-like outgrowths are formed from the ribbon-likemeganucleus of an arm or of a part of tlie stolon. These grow,and ns the outline of the gemmula is developed become con-stricted at the base, and ultimately the knob or knobs areseparated off. The granules in the constricted part of theoutgrowth become elongated, spindle-, or rod-shaped (fig. 20)during the constriction, but regain their spherical form assoon as the meganuclei of the gemmulae are free. No distinc-tion whatever can be drawn between the minute structure ofthe meganncleus where it is giving off these branches and thatof other regions — in other words this division is purelyamitotic. But it is not only amitotic, it is obviously unequal.In the amitotic division of the megauucleus of many Ciliataand of some Acinetaria (e. g. Dendrocometes) the divisionmay be an equal division, the two products of fission in theformer case, and the parent and gemmula in the latter mayreceive an equal portion of the parent meganuclear substance.In the case of Dendrosoma it is obvious that the gemmulareceives only a small part of the total meganuclear substanceof the parent. The meganucleus not only divides in gemmulaformation but occasionally in ordinary vegetative growth,as is shown by fclie fact that the meganuclear bands aresometimes discontinuous. We have no reason to believethat this division is brought about by any other process thansimple constriction.

The fragmented or disintegrated condition of the mega-nucleus may be seen in many preparations. It is by nomeans confined to the parts of the raeganucleus in the stolon,but may occur in the basal portions of the arms. In somecases scattered chromatin granules (fig. 12) may be seen inthe cytoplasm in regions where a distinct but not well-defined meganuclear band occurs, but in other regions thewhole of the meganuclear structure appears to be scatteredin the cytoplasm (fig. 1.3). If it is a fact that the mega-

DENDROSOMA RADIAN'S, EHRENBEBG. 157

nucleus under certain circumstances breaks up and is dissi-pated in the cytoplasm, we are reminded of the condition,long ago described by Grnber, of the meganuclear fragmen-tation in the ciliata,, Oxyt r i cha and Lacryrnar ia . Analternative hypothesis, however, might be put forward to theeffect that the condition we have observed is not disinte-gration but construction of meganucleus; that the scatteredgranules we have observed were not cast out from the mega-nnclens, but are in process of formation in the cytoplasm, andwill be added to the nuclear bands.

This alternative hypothesis will be considered more fullyin a, subsequent paper, but whatever hypothesis we adopt thestudy of the sections exhibiting this fragmented conditionconfirms most definitely the statements we have made above—that (1) there is no true nuclear membrane, and (2) that thegranules of chromatin are not connected by a plastin net-work.

MICRONUCLEI.

The micronuclei of Dendrosoma have not been previouslydescribed. Their distribution in the arms and stolon variesa good deal, and it seems very probable that they are notconstant in position but move about in the arms and stolon,driven hither and thither by the protoplasmic currents. Onthis point, however, we cannot speak with certainty as wehave never been able to recognise the micronuclei in theadult living specimens. We have been able to distinguishthem in some of the living gemmulse.

They are not difficult to see in some of the ordinary stainedwhole mount preparations, although the crust of foreignbodies adherent to the pellicle sometimes interferes with theclear definition of the smaller internal structures.

The micronuclei may occur both in the arms and in thestolon. We have not observed them at any time very closeto the distal extremity of the arms, although in one or twocases we have seen one or two micronuclei lying just beyondor close to the distal termination of the raeganucleus (fig.50,in.,

VOL. 5 4 , PART 2. NEW 8J5RIES. 12

158 SYDNEY J. H1CKS0N AND J. rL'. "WADSWOBTH.

and text-fig. A, mi.). The arrangement o£ the micronucleiinthe arms and stolon is very irregular. In some specimens theyare found at fairly regular intervals of 30 JU or 40 fi in the arms,in others they seem to be in pairs (figs. 9, 10), indicating,perhaps, a recent epidemic of division, but in several speci-mens we have found clusters of three, four, five, or sis micro-nuclei irregularly scattered in the arms and stolon. In thespecimens from Birmingham we have noticed that, as a rule,more micronuclei are present than in the specimens from theBridgewater canal. In the clusters there are sometimes eightor nine micronuclei together, and in one specimen therewere as many as nineteen (fig. 15). This irregularity in thearrangement of the micronuclei has suggested the view thatthey may move about in the living organism.

In Dendrocometes and in other Acinetaria the micronucleiare usually surrounded by a clear area, the "hyaloplasm" ofMaupas (fig. 14). Such a clear area is also seen round manyof the microuuclei of Dendrosoma, but it does not appearto be so constant in character as it is in some of the othergenera. In a former paper (16) it was suggested that thisclear area may be due to a shrinkage of the micronucleus inpreservation, and therefore of the nature of an artefact.

This view is confirmed by a careful examination with highpowers of the area round the micronucleus of Dendrosoma,as it shows not the faintest trace of protoplasmic structureeven in the most successfully stained preparations. Occa-sionally a few very delicate strands may be seen stretchingacross the area (fig. 14), indicating, perhaps, a formerorgauic connection between the nucleoplasm and the sur-rounding cytoplasm. But in addition to the perfectly clearand unstainable area we can also distinguish a more irregulararea of cytoplasm around each micronucleus, which is betterdefined in some cases than in others (fig. 13), that differs fromthe rest of the cytoplasm in being relatively free from granulesand stains rather less deeply. It is this outer area whichserves as a guide to the micronuclei and serves to distinguishthem from other chromatin granules.

DENDROSOMA BADIANS, EHRENJ3EKG. 159

The minute structure of the resting micronuclei is verydifficult to determine as they stain so deeply; but we havesatisfied ourselves that there is a definite nuclear membraneand a network of chromatin (figs. 22, 23).

The rest ing micronuclei are always spherical in form.When seen in pairs and clusters they are about 3-3ft indiameter; when isolated they are sometimes as large as 4-5/.iin diameter. Various stages in the division of the micro-nucleus have been observed, ba t others are missing. Ouraccount of the process is not, therefore, quite complete.W h a t we have seen may be regarded as a modified form ofmitosis. I t cannot be positively asserted tha t a more directmode of division of the micronuclei does not take place, butas the different stages of division have been seen in areaswhere gemmule formation has begun, and also in areas wherethere is no evidence tha t gemmule formation is about to takeplace, and as, moreover, we have never seen any signs ofdirect division in the hundreds of micronnclei we haveexaminBd, it seems probable that amitotic division of themicronuclei never occurs.

The history of the mitosis so far as we can judge at presentis as follows: The micronucleus swells and then becomesslightly oval in outline (fig. 24). The smallest specimen wehave seen at this stage is 9-3f.i by 5'1/u. I t is difficult todetermine whether the chromatin network has broken downat this stage or not, bu t definite lines can be distinguishedrunning in the direction of the longer diameter. In thenext stage the oval shape is changed to a spindle shape andthe size is I S ' 3 ^ by 6'8/i (fig. 26). The chromatin seems tobe withdrawn from the points of the spindle, which areusually quite clear at this stage. The chromatin is iu theform of a large number of minute granules connected by anetwork of fibrils. I t is possible tha t we have missed astage here, as we have not found a spindle form yet with thechromatin collected together more definitely into an equa-torial band.

W e have found three or four examples of a stage in the

160 SYDNEY 3. HIOKSON AND J. T. WADSWORTH.

mitosis shown in fig. 25. In this stage the chromatingranules are arranged in lines running from the poles towardsthe equator, but there is a clear zone free from chromatinrunning through the equatorial belt. The three examples ofmicronuclei in this stage we have found measured 6'8 /iby 6'3/(, 8'5/u by 5'6 fi, and 6-8^t by 5'7 ^ respectively.They are oval or nearly spherical in shape. Being small andless pointed than the examples we have seen of the stageshown in fig. 26 it might be supposed that they come earlierin the mitosis. On the other hand, the separation of thechromosomes leaving a clear zone in the equator suggeststhat the metaphase has begun. If this is the correct inter-pretation of them then it seems probable that the onset ofthe metaphase is accompanied by a contoaction of thefigure.

' In the next stage the chromatin granules are collected intwo groups at the poles of the figure, which is 14-5 ju by 4 /.i insize (fig. 27). In the broad band connecting these polesdefinite plastiu lines can be distinctly seen. In the neststage we have observed the poles are further apart, the totallength of the figure being 20-4/.i (fig. 28). The poles are5'1 /.i in diameter and contain an immense number of evenlyscattered minute chromatin granules, but we have not beenable to discern any plastin network connecting them. Theband connecting the two poles has shrunk in the middle to3'5 fi in diameter. The same plastin lines may be seen inthis band as in the last stage. In the final stage (fig. 29)the chromatin granules are more concentrated towards theinner hemisphere of each pole and there is an appearance ofa " pole-plate" similar to that of Paramecium. The spindleis much narrower. Our examples of this stage are smallerthan those of the last named, the measurements of the examplefigured being—total length 15-6 ju, diameter of the poles3"4^, diameter of the spindle 1*7 /x.

The history of the division of the raicronuclei of Dendro-soma that we have just described is different in many res-pects from that we described in Dendrocometes in 1902; but





















DENDEOSOMA RADIANS, EHRENBEEG. 161

it must be remembered that in the case of Dendrocometes wedescribed only the division of the microuuclei in conjugation.The mode of division of the micronuclei in geinmule-forma-tion in Dendroinetes differs in some respects from that seenin conjugation. On this subject we hope to write a furtherpaper at a later date. We have not yet been fortunateenough to observe any phase in the conjugation of Dendro-soma.

It is possible that the minute granules of chromatin seenin various stages of the division of the micronucleus inDendrosoma represent the chromosomes. With this view inmind we have carefully compared them in the earlier andlater stages of the process to determine whether they aredouble in character before their separation in the two poles.In a recent paper Calkins and Cull (4) have shown that inthe earlier maturation divisions of the micronuclei of P a r a -m e c i u m a u r e l i a the chromosomes divide longitudinally.We can only state that we have not been able to find anyevidence that the chromatiu granules in these karyokineticfigures of Dendrosoma divide at all. Evidence of this,however, may be forthcoming from the stages we havemissed.

THE GEHMULJK.

The gemmulas were first discovered by Levick, but it isdifficult to understand from his figures what is their exactshape. If his fig. 4 is drawn accurately to scale thegeiumulait represents was about 45 n in diameter. Kent describes thegemmulse as " hypotrichously ciliated embryos of relativelylarge size." Unfortunately he gives no statement of the size,but according to his figure they are about 33"3 /x in diameter.

Sand repeats Kent's statement that these bodies are hypo-trichous, but adds that they are " en forme de lentille bicon-vexe aplatie," and have three contractile vacuoles (in corre-spondence with Kent's figure).

In the living material we have examined from the Bridge-

162 SYDNEY J. HIOKSON AND J. T. WADSWORTH.

water canal two kinds of free-swimming gemmulae wereobserved : a large kind which was plano-convex in sideview (fig. 1), provided with a band of several rows of cilia andfrom six to ten contractile vacuoles; said a smaller kind(fig. 31), biconvex or loaf-shaped in side view, with anequatorial band of three or four rows of cilia iind providedwith only three or four contractile vacuoles.

In this material, however, we have found the Acinetariaattributed to the genera T r i c h o p h r y a and LernEeophryaassociated with Dendrosoma, and until recently we had nodefinite evidence as to which of the three forms the gemmulsebelonged.

In the material obtained from Birmingham no Tr icho-phrya nor LernEeophrya. forms were found, and thegemmulse we found were all of the larger plano-convex type(fig. 1). This observation suggested that the larger typeis the geminula of Dendrosoma; but we obtained a definiteproof of the truth of this suggestion by our observations onthe development of two of these geminula3 into the definiteDendrosoma forms as described below (p. 167).

We then examined carefully all our whole mount prepara-tions for Lernaeop hrya forms showing geminulas in thebrood-pouches, and found that the smallest of them was 24 nin diameter, and the largest about 37 fj. (the outline of thisgenimula is indistinct and the measurement probably not quiteaccurate). The average diameter of eleven gemmulEe worksout at about 29'6 f.t. The measurement of a larger number ofgemmulas of Dendrosoma, in their brood-pouches, gave usconsiderably greater diameters, but there are one or twocomplications that must be mentioned before giving the actualfigures obtained. Whereas all the Lern teophrya gemmulaswere approximately circular in outline, many of the geinmulasof Deudrosoma, in the aspect presented to us in the fixedpreparations, were definitely oval in outline.

The smallest of the fully formed gemrnuke was 29'6 fi(circular in outline), the largest 407 fi by 55"5 fx (oval in out-line). Many of the gemmulce we measured were not fully

HJSNDB0S0MA..1UDIANS, EHttENBERG. Jb"3

formed, and it may be that the size was not as great as itwould be when the outline was completed. There is no reasonto believe, however, t ha t there is any considerable growth inthe geinmula after the first faint lines marking out its contourare noticeable.

The average of the shorter diameters of sixteen gemrnuliowas about 3 5 5 ju and the average of the longer diametersabout 41 /x. W e may roughly express, therefore, the diffe-rence in size between the two kinds of gemmulce as a differenceof 29:6 ;u by 29-6 n in L e r n a e o p h r y a and 35'5 /.i by 41 /x inDendrosoma. There is not much difference in size, probably,between the largest gemmulte of L e r n a e o p h r y a and thesmallest gemmulse of Dendrosoma, and there is clearly con-siderable variation in the size of the gemmulae of bothgenera.

But still it may be considered a fact of some systematicvalue that the gemmulse of Dendrosoma are larger than thoseof L e r n t B o p h ry a. W e found, unfortunately, no T r i c h o -p h r y a forms showing formed gemmulas, and we can thereforegive no near details of them. They have been described byBiitschli, Sand, and others, but we have not found anymeasurements given of them in the l i terature of the genus.

The gemmulse of Dendrosoma are usually found in well-developed individuals, and ai-e frequently situated at thebase of the arms (text-fig. A), but they also occur in thecourse of the arms and more rarely in the stolons.

The gemmulse at the base of the arms is a very character-istic feature of the specimens from the Bridge-water- canal. l athe specimens from Birmingham the gemmiilas are morefrequently found some little distance above the base.

In the earliest s tage of gemmule formation there is a s l ightswelling in the arm, and two or three curved lines (fig. 19, o.)appear in the cytoplasm and mark the external boundaryof the future gemmula. A narrow crescentic space oftenappears between these lines and the cytoplasm. The mega-nucleus sends off a short branch which ends in a knob-likeswelling towards the concavity of these lines (fig. 20). The

164 SYDNEY J. HICKSON AND J. T. WADSWORTH.

base of tin's artn of the meganucleus gradually becomes con-stricted, and at a later stage divides, leaving the knob-likeexti-emity as the meganucleus of the gemmula (conf. p. 156).

In several cases, particularly in specimens from Birming-ham, we have observed two of these processes entering intothe gemmula area, and we have several preparations of younggemmulas with two distinct meganuclei (figs. 16 and 21) •When there are two meganuclei in one gemmula there seemsto be a great deal more ineganuclear substance in proportionto the cytoplasraic substance than when there is only onemeganucleus. A comparison of the different gemmulse withonly one meganucleus renders it difficult to believe that thereis any definite relation between the cytoplasm and nucleoplasmin gemmule formation.

One or two, or possibly in some cases more than twomicronuclei in the vicinity of this swelling increase in sizeuntil they are about 11 /x in diameter. One, or possibly morethan one of them, becomes spindle-shaped, attaining to asize of nearly 14 /i in length by l l juin greatest diameter(fig. 19). This micronucleus then divides by mitosis (see p.159).

While the micronucleus is thus dividing the boundary linesof the gemmula are in the process of completing the enclosureof the gemmule area. The division of the micronucleus is,however, completed, and the daughter-nuclei have consider-ably shrunk some time before the area of the gemmule isentirely delimited from the protoplasm of the arm.

It is not possible for us to state definitely that there is anyconstancy in the number of micronuclei taking part in thebud formation.

In the bud that is still in the brood-pouch, shown in fig. 17,there is only one micronucleus. In the specimen shown infig. 19 two micronuclei are taking part in the formation ofthe gemmula; in the young form shown in fig. 18 there arethree micronuclei (only two are drawn, the third being hiddenby the meganucleus) ; in that shown in fig. 21 there are four,and in that shown in fig. 16 there are seven. We have never

DJSNDKOSOJIA KADIAKS, EHUENBJBJRG. 165

seen any evidence of division of the micronucleus during thefree-swimming gemmula stage nor in younger fixed si ages.I t seems probable, therefore tha t the number of microuucleitakiug part in the formation of the bud may vary from oneto seven. In Dendrocometes we also found that thenumber is not constant, but varies from two to five.

In Dendrosoma then, as in Dendrocometes , the megn-nucleus of the gemmula is lonned by amitotic division of tliemeganucleus of the parent, and the micronuclei of the gemmulaare formed by mitotic division of the micronuclei of theparent.

THE FKEK-SWIMMIKG GEHJIUJ,A.

We have called attention to the fact that there is consider-able variability in the size of the gemmuJce of Dendrosoma.The gemmula shown in fig. 1 was plano-convex in form, witha broad girdle of several rows of cilia extendiug from themiddle almost to the edge of the plane surface. It was 00/xin diameter and 41)^ in height. It was difficult to count thenumber of contractile vacuoles or to be certain they wereconstant in number, but there were certaiuly more thauthree, and probably from eight to teu. Their rhythmic con-tractions were not synchronous, and frequently, but not con-stantly, two or three vacuoles in close contact made theirappearance when previously only one was seen.

The meganucleus in this form could be clearly seen iu thecentre of the protoplasmwhen the gemmula was viewed fromabove or below. It was sometimes spherical, but varied inshape, and frequently showed oue or two lobate processeslike tlie pseudopodia of an amoeba.

This particular gemmula was kept under observation iortwo days, and gave rise to a young" suctorian, which wasclearly a Dendrosoma r a d i a n s .

The Iree-swimmiug gemmulas of the second kind (p. 161),found in the material from the Bridgewater canal, are pro-bably the geminulaa of the Lerneeopkrya forms. They have

166 SYDNEY J. H1CKS0N AND J. T. WADSWOKTH.

some resemblance to the figures and description oi: thegemmula of Tr ic l iophrya ep i s ty l id i s given by Biitschli(2, Pi. 78, 6 6).

According to Sand, however, the reproduction of Tricl io-phrya ep i s ty l id i s is "par embryons internes, mul t ip les(tous situes dans la me me cavite), en forme de lentille bicon-vexe, munis de 3 couronnes de cils et de 3-8 vacuoles con-tractiles."

According to Stein the four to eight gemmulse that may befound in the brood-pouch oi! this species are produced by thefission of a single gemmula.

We have not observed more than a single gemmula in anybrood-chamber of either Lernffiophrya or Dendrosorna,but we have not seen enough specimens of Tr ic l iophryayet either to affirm or deny Sand's statement that the gem-malss are multiple in that genus.

The gemmnle formation in the specimens of. Lernaeophryaresembles that described by Perez (25) for the specimensobtained by him at Bordeaux in the curious fact that it some-times occurs very early. In our figure (32), for example, wehave drawn an example of a very young Lernaeophrya (orTr ic l iophrya '!) which has only just settled down, but alreadyshows a fully formed gemmula in the brood-pouch.

We cannot give a decided opinion as to whether all thefree-swimming gemmulse of this biconvex type belong toLernsBophvya or to T r i c h o p h r y a , as we have not atpresent been able to trace out their histoi-y after they havesettled down, but it is almost certain that they belong eitherto the one genus or the other, and not to Dendrosuma or anyof the other Acinetaria associated with it.

These gemmulae are usually biconvex, with a slight con-striction in the middle, an equatorial band of four rows ofcilia, and three contractile vacuoles (fig. 31). There is pro-bably a considerable range of variation (see p. 162) in sizeand shape. One of the convex sides is sometimes rather moreflattened than the other ; there may be only three, or possiblymore than four, rows of cilia in the equatorial band (the exact

DENDROSOMA RADIANS, JSHllENBEllG. 167

number of rows being difficult to determine unless the gein-mula is seen sideways and the cilia are moving slowly). Thenumber of contractile vacuoles may in some cases be two orfour, but is usually three.

A remarkable point in the structure of these gemuiulse isthat at present we have no definite evidence of the presenceof micronuclei. Neither in the free-swimming gemmu188themselves nor in the preparations (both whole mounts orsections) of the gemmulaa in the brood-chambers, nor in thebody of the Leruasophryas and T r i c h o p h r y a s have webeen able to find the inicronuclei in any form.

Certain deeply stained granules are sometimes foundscattered in the protoplasm, and some of these may be, andprobably are, micronuclei. It is very improbable that theseor any other Acinetaria are not heterokaryote, but we imaginethat in Lernasophrya, and possibly in T r i c h o p h r y a too,the micronuclei are very small or involved with the mega-nuclei.

Further investigation is needful before the mystery of themicronuclei of these forms is solved.

DEVELOPMENT OF THE G-EJIJIOLA.

We have observed the development of the gemmula in theBirmingham material twice. The history of one of these,September loth, 1908, was as follows:

A free-swimming gemmula settled down on the cover-glassbetween 11.45 and 12 noon. The cilia disappeared entirelyin forty minutes, and as they disappeared short suckerswere developed all over the body, except, of course, the partattached to the cover-slip. As to the method of disappearanceof the cilia we have nothing but the negative evidence to offerthat we have not seen them break off. The probability is thatthey are withdrawn. We feel certain that they are not con-verted into suckers. At 12.30 the embryo was in a similarstage to that represented by fig. 3, and closely resembles thestage figured by Biitschli for T r i c h o p h r y a (2, PI. 78, 6 c).

168 SYDNEY J. HIOKSON AND J. T. WADSWOKTH.

It was slightly oval in outline, the two diameters being55*5 fi by 518 fx. A preserved and stained geinmula of thisstage is shown in tig. IS. At 1.80 the tentacles had con-siderably increased in number and in length on one quadrant;of the geinmula, but had diminished in number over the restof its surface. At 2.10 the main body of the gemmula hadincreased to 62 /x in diameter, but on one side a short armprocess (7"2 (x), supporting a great many tentacles, had beenprotruded. There was only one tentacle left on the main body.Six contractile vacuoles were observed at this stage, and themeganucleus was visible and had an amoeboid form with twoshort, thick, pseudopodia-like processes. At 3.10 the armwas 25-9 fx in length and the tentacles confined to its distalextremity. Tor the first time a single contractile vacuolewas seen at the base of the arm.' At 3.55 the arm hadincreased to 33"3 /x in length, and a new arm at right anglesto it was beginning to be formed. At 4.40 the main bodywas losing its circular outline. The new arm, about 14*8 /x inlength, exhibited tentacles, and the first formed arm was48-l jx in length. Three inicronuclei were clearly visible atthis stage in the clear protoplasm. The meganucleus had fourbranches, one directed towards the longer arm, but not extend-ing into it, one towards the shorter arm. Another specimen ofa Dendrosoma, which was probably of the same age as thisone, was found in a whole mount preparation and is shown infig. 21. The meganucleus is in two parts, but the generalform of it, apart from this peculiarity, is very characteristicof young Dendrosomas of this stage. In this particular speci-men there were four well-developed micro nuclei.

The other case of the development of a young Dendrosomafrom a free-swimming gemmula is illustrated by the figures2-7. The ciliated gemmule, at the time it settled down, hadfrom eight to twelve contractile vacuoles. The meganucleuscould be clearly seen, as it was quite colourless as comparedwith the pale yellow tint of the surrounding cytoplasm. Itwas distinctly amoeboid, constantly, but slowly, changingits shape (fig. 2). Before the cilia disappeared numerous

DENDROSOMA RADIANS, EHEENJBEEG. 169

short suckers were produced, scattered irregularly butprincipally near the margin of the body. The body of thisspecimen did not retain its circular form, but became irregu-larly quadrilateral. After a period oE two hours (fig. 4) thecilia had disappeared and the suckers were mainly collectedat the two ends, but two or three odd suckers were observedin the middle. In another Hour there were three distinct tuftsof suckers (fig. 5), but two hours later still all the suckershad disappeared except one isolated one, and a dense tuft atoue end (fig. 6). The next morning, i . e . eighteen hourslater, the end supporting the tuft of suckers had grownconsiderably to form a definite Dendrosoma arm (fig. 7).

The stags just described corresponds with that figured bySavile Kent (in his PI. 47, fig. 21), but differs from it in theabsence of suckers on the general surface of the body. Wehave seen a good many specimens of this stage but never onewhich, possessing a well-defined arm, had suckers scatteredover the rest of the body, as shown in Kent's figure. InKent 's figure of this stage only three contractile vacuolesare shown. Levick, however, gave another figure in whichsix contractile vacuoles were shown. The latter is in thisrespect, as well as in the actual size, more in accordancewith our observations than the former.

T h e s o - c a l l e d " e x t e r n a l b u d s . " — I n the literature ofDendrosoma reference is made by nearly al], authors toanother method of reproduction than that by the geinmultepreviously described. Kent observed at or near the distalextremity of the arms of many specimens a number ofspherical or oval bodies, which he believed to be " exo-genously produced germs similar to those of A c i n e t am y s t a c i n a of Stein." I t is probable that these are thesame bodies as those previously described by Levick as" ovaries." Biitschli describes them as " angebliche freieiiussere Knospen," and Sand as " gemmes externes cilieesquelquefois tentaculees, produites a l'extremite des rameaux."

We have found bodies similar in position, form, and size tothese so-called external buds in our specimens from the

170 SYDNEY J. HIOKSON AND J. T. WADSWOBTH.

Bridgewater caual and from Birmingham, and we have dis-discovered that they are epizoic Acinetarians belonging to thespecies Urnu la ep i s ty l i d i s .

The possibility that the bodies described and figured byKent are different from those we have observed has of courseoccurred to us. It is, however, very improbable that externalbuds could be formed in the position of these bodies for thefollowing reasons :

In the formation of a bud it would be necessary for themeganncleus to take part. The meganncleusof Dendrosoma,however, does not extend as far as the extremity of thebrunches, and could not possibly take part in the formation ofbuds in the position assigned to the " external buds " byRaville Kent.

We have examined a great number of specimens of Dendro-soma from the two localities, obtained at different seasons ofthe year and in varying phases of activity, but we have neverseen any reproductive bodies of the form and in the positionassigned to the "external buds"; but Urnu la ep i s ty l i d i sdoes occur in this position in a large majority of the specimensexamined, and frequently in considerable numbers.

ON UKKULA EI'ISTYLIDIS.

This interesting' species was first described by Olaparedeand Lachmann (5). It is mentioned in their first volume(1858-9), but the reproduction is more fully described in thesecond volume (1860-61). It was found on the stalk of anKpis ty l i s . Owing to the appearauce of a branchingtentacle in one of their specimens these authors regardedUrnula as a Ehizopod and placed it next to the genusE u g l y p h a in the family Actinopliryina.

Engelmann (12) and subsequent authors have, however,agreed that it is an Acinetarian, and Biitschli places it in thefamily Urnnlina with the genera R h y n c e t a and Acine-topsis—an arrangement that is followed by Sand.

Only one species has been described—Urnula ep i s ty l id i s

DENDROSOMA. KADIANS, EHliENBBKG. 171

—and the measurements given by Sand of this species are :Length of test, 20 JU-120JU; diameter of test and body, 15^-80,1.1;diameter of the nucleus, 5^u-15ju. The genus is characterisedby the definite but very thin test, which is usually conical inshape and curved proximally towards the disc of attachment.There are one, or two (rarely more than two) tentacles. Thereproduction is by oblique unequal fission, and the smaller ofthe two products of fission escapes as a ciliate gernmula.

The question whether the species of U r n u la we have foundon Dendrosoma should be referred to the speciesU. e p i s t y -l i d i s or placed in a new species may be open to discussion;but we can find no satisfactory reasons at present for adopt-ting the latter course.

The specimens attributed to U . e p i s t y l i d i s by Sand andother authors are very variable in size (15,u-80/x in bodydiameter), so that the fact that the largest of the specimenswe have measured is not more than 30 /i in this diameter andthe average is about 25 ft does not signify more than that theU r n u l a on Dendrosoma belongs to a small race.

In the original figure given by Claparede and Lachmauuthe two tentacles are shown to arise from the side of thebody turned towards the host. In most of our specimens thetentacles arise from the distal surface or apex, as shown infigs. 35-39. The original figure with the tentacles arisingfrom the sides has been copied in the subsequent papers andbooks, and it seems to be by no means certain that thisorigin is normal in the species. The body may rotate more orless in the test and the appearance shown may be onlytemporary, but we have observed only one or two cases inwhich the origin of the tentacles may have been lateral.

The position of the contractile vacuole was not constant inour specimens. I t is usually situated, as shown in figs. 35-39,near the centre of the distal convexity, but in several speci-mens we have seen it more deep-seated. In the figures of thespecies given by other authors it is shown by the outer side ofthe nucleus. The structure of the test, which is extremelydelicate, appears to be the same as that previously described,

172 SYDNEY J. HICKSON AND .T. T. WADSWORTH.

except that we have observed a slight disc-like swelliug at thepoint of attachment.

After fall consideration of all these points of apparentdifferences, and bearing in mind the possibility of considerablevariation in adaptation to the conditions, we have come to theconclusion that the U r n u l a found on Dendrosoma should bereferred to the species U. ep i s ty l i d i s (Claparede and Lach-mann).

It is not necessary to give a full description of the species,but we will be content with a few remarks on some specialcharacters. The tentacles are the most remarkable features.In the first place they are comparatively rarely seen, the bodyof the U r n u l a being usualljr rounded off within the test andat rest. In the majority of specimens which do exhibittentacles at all only one is seen. When there are two theyusually cross one another as shown in fig. 39.

It is extremely probable that a specimen that at one timeexhibits only one tentacle may at another time exhibit two, oreven three, tentacles. The tentacles of Urnu la differ fromthose of the typical A.cinetaria in two respects. They arerelatively very long and flexible, moving actively with curiousserpentine curves as if in search of food. They do notterminate in a sucker.

When fully extended they are very delicate and attenuateat the distal extremity to a very fine point (fig1. 35). Whenpartially retracted or not fully extended they are much thicker,show a spiral marking (6g- 45), and terminate in a spindle-shaped, or sometimes bluntly club-shaped, extremity. Therecan be no doubt that they are protruded and withdrawn intothe body with considerable rapidity.

We have not been able to satisfy ourselves as to the foodof Urnula . We have frequently observed a tentacle bentover towards the heal of the Dendrosoma, with its pointedend buried among the bases of the Dendrosoma suckers.This attitude suggested that the U r n u l a is parasitic on theDendrosoma, and this suggestion is confirmed by the factthat the heads of Dendrosoma affected by U r n u l a do not look

DENDROSOMA RADIANS, EHB-ENJBEB.G. 173

so healthy as those that are free from them. On the otherhand, healthy Urnu las are frequently found on Dendrosomaitself in positions that would not permit them to penetratethe delicate unprotected ectosarc of the head region, and alsoon other bodies, such as weeds, stalks of Epistylis, etc. Wehave, moreover, never observed a stream of food particlespassing from the Dendrosoma to the U r n u l a body in thetentacle that is apparently attached to the former, as weshould certainly find if the latter were feeding parasifcicallyupon it. We are inclined to the opinion, therefore, that theUrnu la is epizoic and not strictly parasitic.

The meganucleus is usually spherical in shape and centralin position. In one specimen (fig. 40) in which the diameterof the body as preserved was 19 fi, the diameter of the mega-nucleus was 8'5 /u. The chromatin of the meganucleus is usuallyin the form of a network. It never shows the gran ular characterthat is such a marked feature of the meganucleus of Dendro-soma. It is sometimes difficult to determine whether a micro-nucleus is present or not, but a small deeply staining granuleabout 1"7 n in diameter may frequently be observed in sectionswhich we believe to be the micronucleus (fig. 40). ISTo stagesin its enlargement or division have been observed.

We have observed the same method of reproduction inour specimens as that previously described for the speciesby Claparede and Lachmann. The individual divides byoblique fission into two parts, one usually larger than theother (figs. 41, 43). Of these the smaller becomes holo-trichously ciliated and escapes. The larger may remain inthe undivided lorica and increase in size until it is again fullgrown. Of this, however, we have no positive evidence. Itis possible, however, that the escape of the smaller product offission entails the death of the larger product, but if thiswere the case we should expect to find attached to the Den-drosoma a certain number of empty Joricae. We have, how-ever, never found an empty lorica attached to the Dendrosomanor any signs of degenerating protoplasm in a lorica.

The U r n u l a was found on specimens of Dendrosoma fromVOL. 54 , PART 2. NEW SERIES. 13

174 SYDNEY J. HECKSON AND .1. 'I'. WADSWORTH.

both localities. Sometimes a few specimens may be foundthat are quite free from these epizoites, but it is very rarelythe case that a single collection of Dendrosoma is broughtin that does not show some infected specimens. The numbervaries a good deal, but there is no reason to believe thatthey are more numerous at one season of the year than atanother.

The settlement of the gemmula and the development ofthe lorica have been observed by one of us (W.) on two orthree occasions. The free-swimming holotrichously ciliatedgemmula is about 20/xby 15 ft in size. The cilia stop movingand begin to disappear about ten minutes after settlementon the Dendrosoma is effected. The lorica must be formedvery rapidly as the protoplasm is contracted into an ovalform near its free end, as in fig. 35, about five minutes afterthe settlement. The cilia are still plainly visible, but inanother five or ten minutes they disappear. A. single tentaclebegins to grow out a few minutes after the cilia have dis-appeared.

A curious feature that was observed on both occasions wasthe presence of two or three minute capitate tentacles at thetime the cilia are disappearing. They are, however, onlypresent for a few minutes, and cannot be recognised at allwhen the characteristic Urnula tentacle is developed.

In the figure given by Saville Kent one of the supposed"external buds" is drawn with six short capitate tentacles.It is possible that Kent may have observed an Urnula thathad just settled down and still retained the temporarycapitate tentacles we have described.

FURTHER REMARKS ON THE SYSTEMATIC POSITION OF DENDBO-

SOMA, LEENJKOPHEYA AND T R I C H O P H E Y A .

The relation of these three genei-a has already been brieflyreferred to in the introduction, but a further summary of thecharacters that distinguish them may be useful in the lightof the observations we have recorded in this paper.

DENDROSOMA BAD LANS, HKIIENBGIIG. 175

The genus T r i c l i o p h r y a was described by Claparede andLachmann, 1858-61. The original type-species is T .e p i s t y l i d i s , a common species usually attached to the stalkof Epistylis. We have found it frequently in the Bridgewatercanal collections, and the specimen we have drawn in fig.46 Tr. was about 129'5/uby 111/* in size.

Taking this as a type we may say that it differs from afall-grown Dendrosoma in its small size and the relativeshortness of its arms. I t might be thought to be a youngDendrosoma, but it differs from the young Dendrosoma inhaving several short arms instead of only one or two. Theyoung Dendrosomas shown in figs. 47 and 48 are smaller thanthe T r i c h o p h r y a shown in fig. 46, but nevertheless exhibitthe characteristic Dendrosoma form.

There must also be some important difference between themin the character of the micro-nucleus, but the nature of thisdifference we cannot describe. I t is perfectly easy, as ourfigures show, to demonstrate the presence of micro-nuclei inyoung Dendrosoma, but we have not yet been able to finddefinitely the inicronucleiis in any specimen of T r i c h o p h r y awe have examined.

In T r i chophrya ep i s ty l id i s , according to Stein,Biitschli, Sand, and other writers, the single gemmula that isformed in the brood-chamber may divide into four or eightgemmulae before liberation. We have not observed a similarmode of reproduction either in Leriiasophrya or in Dendro-soma.

The figure given by Biitschli of the free-swimminggemmula of T. ep is ty l id is shows that it must be verysimilar in shape to the gemmula we have ascribed toLernasophrya (fig. 31).

Several other species of the genus have been described bySand and others, bat of these we have very little detailed infor-mation. Some of them, such as T. sa lparum, T. amoe-boides, T. odontophora and T. mirabi l i s are marine.One of these at least, T. mirabi l i s , found attached to hydroidsat Banyuls, may possibly be more closely related to the genus

176 SYDNEY ,T. HICKSON AND ,T. T. WADSWORTH.

Lernseophrya as it is charactei'ised by its very longsuckers.

The genus Lernseophrya was described in 1903 byPerez (25). We have found it in the Bridgewater canal, and,like the Bordeaux type-specimens, attached to Cordylo-pliora.

Lernaeophrya is a larger form than Trichophrya.According to Perez it may attain to a size of 400ju—500;u.Our specimens are not as large as this, but we have foundthem over 200^ in length (fig. 49).

They differ from both Trichophrya and Dendrosomain the extraordinary length of the suckers. Perez says hehas measured suckers 400 m in length. Our specimenswere smaller than his, but we have found some of thesuckers to be over 275 f.i in length. Perez states that the gem-mulse are frequently formed at a very early stage, before thearms are formed. We have found the same peculiarity in someyoung forms which we attribute to Lernseophrya. In ourfig. 32 we have drawn a young Acinetarian, which is probablya young Lernseophrya, although we have no conclusive evi-dence to prove that it is so, in which there are no arms andonly four suckers, bnt it nevertheless contains a full-growngemmula in its bi'ood pouch.

As in Trichophrya so in Lernasophrj^a the micronucleihave at present escaped our observation, and as Perez does notmention these structures in the description of his specimensit is possible that some peculiarity of the micronuclei, whichrenders them obscure in the resting stage, is a characterwhich Lernfeophrya and Trichophrya have in common.

Only the one species, L.capitata Perez, has at presentbeen described. Our specimens do not appear to differ fromthe type except in size, and we are inclined, therefore, toregard them as a small race of the type-species.

The gemmulse desci'ibed by Perez were 50 /x in diameter,whereas the largest we have measured were only 37 /t indiameter, but in other respects they seem to agree.

The important characters in which the genus Dendro-

JlJKNDllOSOJIA. H.AD1ANS, JiKKJiNBEliG. 177

soma differs from T r i c h o p h r y a and Lernseoplirya areits greater size, the greater length of its arms, and tliecharacters of the gemmula. The suckers of Dendrosoinavary a great deal in length, according to circumstances, butthey never attain to the same actual or relative length as thesuckers of Lemasophrya . The free-swimming gemmula!of Dendrosoma differ from the gemmulas which we attributeto Lernaeophrya in size, in shape, in having several insteadof only three or four bands of cilia, and in having severalcontractile vacuoles iustead of only three.

A prolonged study of the specimens of Dendrosoma fromthe Bridge water canal and from Birmingham give somegrounds for the view that they belong to different species.

These differences have been previously mentioned (p. 147);it is only necessary in this place to refer again to the differencein the number of the micronuclei. In looking through anumber of preparations of specimens from the two localities,the large number of the micronuclei in the Birmingham speci-mens is often a very striking feature. To take two extremecases, the piece of an arm that is drawn in fig. 15 showingnineteen micronuclei in a cluster round the meganucleus, anda gemmula showing seven micronuclei, such as that drawn infig. 16, we should recognise at once as belonging almostcertainly to the Birmingham variety. On the other hand,when the micronuclei are isolated or in pairs at considerabledistances apart, as shown in text-fig. 1 and in figs. 9 and 10,there would be a strong probability that they were taken fromspecimens of the Bridgewater canal variety.

But nevertheless specimens of the caual variety are some-times found iti which several micronuclei are aggregatedtogether, as shown, for instance, in fig. 8, where six micro-nuclei form a cluster, and iu many specimens from Birming-ham the micronuclei are scattered in very much the same wayas in the canal variety.

To endeavour, therefore, to make a specific character of thenumber of the micronuclei, a character which is obviouslysubject to great variation, would be a task of great difficulty

178 SYDNEY J. HICKSON AND ,1. T. WADSWORTB.

and very little pi-actical value. Joseph (18) has shownthat there is a great range of variation in the number ofmicronuclei in the Ciliate Loxodes, and it is clear from thisand from other evidence that it is not safe to base specificdifferences on the number of the micronuclei.

SUMMARY OF RESULTS.

Specimens of Dendrosoma were found in the Bridgewatercanal attached to C o r d y l o p h o r a , Polyzoa, and weeds. Theydiffer in some respects from the type of D e n d r o s o m ar a d i a n s , and may be regarded as constituting a distinctrace.

The meganucleus does not extend to the extremity of thearms as previously described and figured. It has no truenuclear membrane aud no linin or plastin supporting network,but consists of numerous chrotnatin granules, " chroimdia/1

floating freely in a nuclear sup.

There are numerous micronuclei, usually about 4 /i indiameter, which divide by mitosis. Reproduction is effectedby the formation of internal buds, " geramulse." They areplano-convex in form, 35"5 x 41 ft in diameter, have severalcontractile vacuoles aud a broad band of cilia. The descrip-tion of these gemtnulae given in this paper differs in somerespects from that of previous authors.

The gemmulse of L e r n s e o p h r y a are also described.The development of the gemmulse of Dendrosoma is

described.The "external buds" of Saville Kent are proved to be

epizoic Acinetaria belonging to the species U r n u l a epi-s t y l i d i s .

LITERATURE.

1. Awerinzew, S.—" Astrophiya arenaria," ' Zool. Anz.,' xxvii, 1904,p. 425.

2. Biitsolili, ().—"Protozoa. Abt. iii, Infusoria," in Bronn's ' Klassenu. Ordnnngen,' Leipzig, 1887-89.

DENDROSOMA. RADIANS, EHKKNBBEG. 179

3. Calkins, G. N.—" Protozoa," Columbia University, ' Biol. Series,'1901.

4. and Cull, S. W.—"The Conjugation of Pararnieciumaurelia," ' Arch. Protist.,' x, 1907.

5. Claparede, E., and Lachmann, J.—' iiltudes sur les Infusohes,'Geneva, 1857-1861.

6. Collin, B. — "Note preliminaire sur un Acinetien nouveau,Dendrosomides paguri ," 'Arch. Zool. Exp.,' (4) v, 190(>,p. 64.

7. "Note preliniinaire sur quelques Acinetiens," ibid., (4), vii,1907. Notes et Revue.

8. Delage, T., and Herouard, E.—' Zoologie Concrete Protozoa,' 1S98.9. Ehrenberg, C. G.—" Uber eiue neue Thiergattung," ' Monats.

Ak. Berlin,' 1837, dec. 11, p. 152,10. " Polygastrica exckisisBacillaries," ibid. , 1840, p. 199.11. " " Uber die seit 27 Jahren noch wohl erhaltenen Organisa-

tions Priiparate," ' Abh. Ak. Berlin,' 1862, plate iii.12. Engelmann, W.—" Zur Naturgeschichte der Infusionsthiere,"

' Zeitschr. wiss. Zool.,' xi, 1862, p. 370.13. Entz, G. (sen.)—" TJeber einige Patagonische Protozoen," 'Math.

natuvw. Bev. Ungarn,' xxi, 1903, published 1907.14. Greenwood, M.—" The Macronucleus of Carchesium," ' .Tourn.

Physiol.,' xx, 1896, p. 427.15. Hickson, S. J.—" Heterokaryota " in Lankester's ' A Treatise on

Zoology,' part i, fasc. 2, 1903, p. 421.16. and Wadsworth, J. T.—" Dendrocometes paradoxus ,"

Part 1, ' Quart. Journ. Micr. Sci.,' 45, 1902, p. 325.17. " Note on the Structure of Dendrosoma rad ians , "

' Rep. Brit. Assoc.,' 1908, Dublin.18. Joseph, H. —" Beobachtungen iiber die Kernverhiiltnisse von

Loxodes," ' Arch. Protist.,' viii, 1907, p. 344.19. Saville Kent.—' Manual of the Infusoria,' 1881-2.20. Lang, A.—" Lehrbuch der Vergleichenden, Anatomie," ' Pi-oto/.ou,'

1901.21. Lankester, E. R.—Article " Protozoa," ' Zoological Articles,' 1891,

p. 36.22. Leidy, J.—"Notice of some Fresh-water Infrisoria (Cothurnia

and Dendrosoma)," ' P. Ac. Philad.,' 1874, p. 140.23. Levick, J.—" On Dendrosoma r ad i ans , " ' Midland Natural.,' iii,

1880, p. 29.

180 SYDNEY J. H1CKSON AND J. 'I.'. WADSWORTH.

24. Martin, C. H.—"Some Observations on Acinetaria," ' Quart. Journ.Micr. Sci,' 53,1909, p. 353.

25. Perez, Ch.—" Suv un Acinetien Nouvean,' ' C.R. Soc. Biol.,' 1903,p. 98.

26. Sand, R.—' Etude monograpliique des Infusoires tentaculiferes,'Brussels, 1901.

27. Stein, Fr.—' Der Organismus der Infusionsthiere,' Leipzig, 1868.

EXPLANATION OP PLATE X,

Illustrating the memoir by Messrs. Hickson and AVadsworthon Dendrosoma radians.

LETTEBING.

A. Arms of Dendrosoma. ehr. Ohromatin granules, c.v. Contractilevacuoles. D. Swollen end of the arm of Dendrosoma in fig. 30.E. Euplotes. Ep. Epistylis. g. Gemmula in brood-pouch. M. Mega-nucleus. M.g. Meganucleus of gemmula. TO. Micronucleus. O. Out-line of gemmula in fig. 19. s. Sucker, st. Stream of food-particles.t. Tentacle of Umula. Tr. Trichophrya in fig. 45.

Tigs. 1-7.—Illustrating the free-swimming gemmula of Dendrosomaand its development after fixation.

Pig. 1.— Side view of the free-swimming gemmula, showing theband of several rows of cilia and four of tlie peripheralcontractile vaouoles. x 250.

r ig. 2.—Surface view of a gemmula immediately after fixation.The meganucleus (M.) has an amoeboid form.

Fig. 3.—Gemmula as seen about thirty minutes after fixation,showing the suckers (s.) that have begun to sprout outfrom the general surface. Cilia are still present butcomparatively few in number.

Fig. 4.—Young Dendrosoma two hours after fixation.Fig. 5.—-Young Dendrosoma tkree hours after fixation.Fig. 6.—Young Dendrosoma five hours after fixation.Fig. 7.—Youug Dendrosoma one day after fixation. All the

suckers are now confined to the extremity of the single arm.Fig. 8.—Section through a part of the stolon of a Dendrosoma showing

a cluster of six micronuclei (in.).

JOBNDEOSOJIA J1ADIANS, EHBENBtfRU. 181

Tig. 9.—Section through an arm on the same slide showing themicronuclei in pairs. Each of these micronuclei are about 3-5 fi indiameter.

Fig. 10.—Section through another arm in the same preparationshowing another pair of micronuclei and a contractile vacuole.

Fig. 11.—Section through a portion of a stolon showing a doubleand contorted meganucleus.

Fig. 12.—Section through a portion of an arm showing chromatingrains scattered in the cytoplasm. M., the main meganucleus.

Fig. 13.—Section through another part of an arm showing a singlemicronucleus (in.) about 4 /t in diameter and the fragmented meganucleus.

Fig. 14. — Section through another arm more highly magnified toshow the structure of the cytoplasm and nuclei. The micronucleus is3'2 fj. in diameter, the largest chromatin granules in the meganucleusabout 15 ii in diameter.

Fig. 15.—Drawing of a part of the arm of a whole-mount preparationof a specimen of Dendrosoma from Birmingham showing a cluster ofnineteen micronuclei.

Fig. 16. — Section through a gemnrula of Dendrosoma fromBirmingham showing two distinct meganuclei (Mg.) and seven micro-nuclei (in.). The diameters of this gemmula were 55 /i x 48 /».

Fig. 17.—Transverse section through an arm showing a newlyformed gemmula in position. The meganucleus of both the gemmulaand of the arm have discharged some chromatin grains (ehr.) into thegeneral cytoplasm. The diameter of the bud is 22 p, of the micro-nuclei about 5-5 p.

Fig. 18.—A gemmula soon after it has become fixed from a stainedpreparation, showing the band of cilia (c.) and two suckers («.). Thediameters of the gemmula are 38 /i X 37 fi and of the micronuclei 5 pand 4'8 /*.

Fig. 19.—An oblique section through an arm of Dendrosoma showingan early stage in the formation of a gemmula. At o. are shown thecurved lines that mark the boundary of the gemmula. Two micro-nuclei of the arm have enlarged previous to division. The sizes of themicronuclei (in.) in this preparation were 153 /i X 6"8yn and 93/i x 51 /trespectively.

Fig. 20.—Transverse section through an arm showing the outline ofa gemmula and the method by which a part of the meganucleus of thearm is pinched off to form the meganucleus of the gemmula. In thispreparation some of the contractile vacuoles could be seen. No micro-nuclei were observed in this section. The diameter of the gemmulafrom a-b was 37'4 /t.

182 SYDNEY S. HICKSON AND J. T. WADS WORTH.

Fig. 21.—Young Dendrosoma observed alive from free-swimminggemmula stage (September, 1908) and then fixed. I t is 85 /* x 70 /i insize, the arms about 20 n in length, and the four micronuclei each about4 fi in diameter.

Figs. 22-29.—Series of stages seen in the mitotic division of themicronuclei. X 1000.

Fig. 22.—A full-sized micronucleus in a resting condition.Fig. 23.—Enlarged micronucleus previous to mitosis.Fig. 24.—Micronucleus in stage of spindle-formation.Fig. 25.—Stage of division in which there is an equatorial band

free from chromatin.Fig. 26.—A stage in mitosis occasionally seen in which the

poles are pointed and free from chromatin. The relationof this stage to tlie other stage in mitosis is not clear(see p. 159).

Figs. 27-29.—The chromatin is, in these stages, collected intothe two poles which are connected by an achromaticspindle.

Fig. 30.—Dendrosoma feeding upon aEuplotes (E.). The swollen endof the arm of the Dendrosoma (D.) was 15 fi in diameter, the length ofthe Enplotes body 100 /*. A stream of particles (Si.) could be seenpassing down into the arm through the attached suckers; the othersuckers were quite indifferent.

Fig. 31.—Side view of a gemmula of Lernseophrya (?) showing twoof the three contractile vacuoles. None of these gemmuhe exhibited amicronucleus.

Fig. 32.—A very young, probably quite recently fixed specimen ofLeriiEeophrya with only four suckers, showing a completely formedgemmula iu position. There are no micronuclei to be seen.

Figs. 33 and 34.—Two sketches of young Dendrosomas showing themethod of arm formation in Dendrosoma.

Figs. 35-39.—Series of studies of U r n u l a ep is ty l id i s epizoic onDendrosoma showing the different forms assumed by the tentacles. Infigs. 35-38 the specimens have only one tentacle, in fig. 39 it has two.

Fig. 40.—Section through an Urnula from a stained preparation. Inthis specimen the diameter of the body is 19 p, of the meganucleus (31.)85 it, and of the micronucleus (m.) 17 p.

Fig. 41.—Transverse section through an Urnula after the formationby fission of a gemmula (y). Drawn to the same scale as fig. 40.

Fig. 42.—A specimen of Urnu l a epis ty l id is , showing the bodyretracted below the mouth cf the test. Copied from Engelniann (5) (PL30, fig. 13).

BJilNPROSOMA KADJANS, EHliUNBEKG. 183

Fig. 43.—Urnula epis ty l id is , showing the formation of thegemmula. Copied from Claparede and Lachniann (5) (PI. 10, fig. 3).

Fig. 44.—Free-swimming gemmula of Urnula. Copied from Claparedeand Lachmann (5) (PL 10, fig. 3).

Pig. 45.—A portion of the body of an Urnu la very much enlarged toshow the spiral marking of the tentacle (t.).

Pig. 46.—A specimen of Tr ichophrya ep is ty l id i s (sp. ?) found inthe Bridgewater canal attached to the stalk of an Epistylis. (From astained preparation.) No niicronucleus could be seen. Size 129 5 ftX lll/u.

Fig. 47.—A very young Dendrosoma with one arm and one micro-nucleus, also attached to an Epistylis stalk. The size of this specimenis 61-3 n in greatest length, including the arm. From a stained pre-paration.

Fig. 48.—Another rather older Dendrosoma with three mieroimclei.Size 60 /i, + the arm 60 /« = 120 p.. From a stained preparation.

Fig. 49.—Lem£eophrya (sp. ?) from the Bridgewater canal. Drawnfrom a living specimen January, 1909.

Figs. 50-52.—Three figures drawn to the same scale (x 1000) toshow the varying structure of the meganucleus of Dendrosoma.

Fig. 50.—Section through a part of an arm (Birminghammaterial) in the region where the meganucleus terminates.The terminal extremity was in the direction of the upperside of the figure, but was not included in the actualsection. Two micronuclei are seen beyond the mega-nucleus. The size of the largest granules was only 0S5p..

Fig. 51.—Section through an arm showing two meganuclearbands. The chromatin granules are smaller than in fig.50, but the meganucleus contains peculiar, large, irregularbodies which give the chromatin reaction.

Fig. 52.—Section through a meganucleus (Bridgewater canalmaterial). The largest chromatin granules seen in thissection are 2'5 p. in diameter.

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