the number and size of glomeruli in the kidneys of fishes, with observations on the morphology of...

THE NUMBER AND SIZE OF GLOMERULI IN THE KIDNEYS OF FISHES, WITH OBSERVATIONS

ONTHEMORPHOLOGYOFTHERENAL TUBULES O F FISHES

JOSEPH NASH Department of Physiology, University and Bellevue Hospital Medical College,

New P o r k City

SIX PLATES (THIRTY-FIVE FIGURES)

A quantitative study of the kidneys of fishes, particularly of the glomeruli, was undertaken, first, because of the lack of information on the subject in the literature; secondly, for the purpose of aiding in the experimental investigation of kidney function, and, thirdly, to study the relationship between the normal habitat of fishes and glomerular develop. ment (Marshall and Smith, '30).

The total glomerular filtration surface of a kidney is of great physiological importance, and its estimation is the ulti- mate aim of a quantitative study of the glomeruli. We may define the total filtration surface as the sum of the surface areas of all the intraglomerular capillaries in the kidney (Vimtrup, ,as). It depends on, 1) the number of glomeruli, 2) the size of the glomeruli, and, 3) the degree of branching of the capillaries within the glomerular tuft. The present investigation consists of the enumeration of the glomeruli in various species of fishes, and a study of the amount of capillary branching within the glomerular tuft. The size of the glomeruli could not be measured by the methods here employed; this factor has been determined for many species of fishes by Marshall and Smith ('30), and some of their measurements are here employed in calculating total filtration surface areas. The opportunity of observing complete

425

THE AMRRICAN JOURNAL OF ANATOMY, VOL. 47, NO. 2

426 JOSEPH NASH

kidney tubules presented itself in the course of the work, and camera-lucida drawings to scale were made of such tubules. Inasmuch as there is very little on the morphology of tubules of fish kidneys to be found in the literature (Audige, '10; Edwards, '28 ; Marshall, '30), these drawings are presented.

MATERIAL AND METHODS

Only sexually mature individuals were studied. In preparation for counting glomeruli, blood was washed out of the vascular system of the surviving fish by injection of an isotonic solution of sodium chloride containing a trace of sodium nitrite. Then a fresh mixture of 13 per cent potas- sium-ferrocyanide solution and 1+ per cent ferric-ammonium- citrate solution, equal parts, was injected. These injections were made into the ventral aorta or into the dorsal aorta with equally good results. Good injections were obtained by ligating the ascending aorta, excising the heart to allow escape of fluid, and then amputating the tail and injecting into the dorsal aorta in a retrograde direction. The kidneys were then excised and placed in a mixture of equal parts of con- centrated hydrochloric acid and distilled water for seventeen to twenty hours. For teasing out of tubules, the kidneys were macerated for fourteen to seventeen hours. Then they were washed free of acid and placed in distilled water, to which a crystal of thymol was added, for twenty-four hours. Small portions of macerated kidney were then transferred by means of a pipette to ruled Syracuse dishes, and the intact glomeruli, rendered conspicuous by the Prussian blue within their capillary tufts, were counted under the dissecting microscope. Successive portions being thus examined, all the glomeruli in the entire kidney were counted.

A solution containing 1 per cent sodium citrate and 4 per cent sodium nitrite, suggested by Dr. Homer W. Smith, when used as a 'wash fluid,' gave good results, in some cases better than saline. Also, good injections were obtained when the Prussian-blue reagents were used in coiicentrations up to 4 per cent.

GLOMERULI IN THE KIDNEYS OF FISHES 427

On mixing thoroughly the suspension of macerated kidney substance and abstracting a known fraction of the total volume for count, it was found that the number of glomeruli calculated for the whole kidney from this fraction agreed, within an error of 5 per cent, with the number found by actual count of the entire kidney. Some of the glomerular counts here reported are calculated on the basis of such fractional counts; approximately 5 per cent of the total kidney substance was subjected to actual count in each case. All complete counts are so indicated. 9 complete count of the kidney of the water frog, per-

formed as a check on the method, agreed with reliable counts on this species done by other methods by previous investi- gators. Incidentally, counts were done on two other species of Amphibia.l

Observations on the size of glomeruli in macerated prepa- rations are worthless because of the swelling which occurs, the extent of which varies according to many conditions, espe- cially the length of time the preparation stands. Thus glomeruli of the cod, which were so small as to be uncountable when first prepared, had increased in diameter 200 to 300 per cent after standing for three months. Though some shrinkage occurs during fixation, measurements made from sections are more reliable, because the method of preparation is uniform. To determine the amount of skrinkage and whether proportionate shrinkage occurs in glomeruli of different orders of magnitude, three species (brown tang, grouper, and catfish) were compared. I n each of these, ten glomeruli were teased out from the fresh kidney in normal saline solution, and their diameters were measiired bp camera-lncida scale drawings. A closely adjacent portion of

The results of complete glomerular counts on three Amphibia were as follows: One Number of

Rody kidney glomeruli Common weight, ' weight, in one

Species name Familu gram8 grams kidney Raua sp. Frog Ranidae 50 ,128 2254 L Bufo americanus Holbrook Toad Bufonidar 50 ,125 2262 I> Siren lacertina Linnaeus Siren Sirenidae 560 .7 9096 1,

8333 R The unidentified frog, Rana sp., represeiits some one of the species of Ranidae

inhabiting Mount Desert Island, Maine.

428 JOSEPH NASH

WEIGHT, QRAM5

195 630 240

each kidney was fixed by Bouin’s method and sectioned, and in the sections ten glomeruli were measured for each of the three species. The ‘diameter’ of a single glomerulus is taken as the average of its maximum and minimum diameters. Comparison of the fresh and fixed glomeruli as to size is shown in table 1; an average shrinkage of about 15 per cent is indicated.

For the most part, glomerular counts were made on only one or two individuals of each species, and the average glomerular diameter was determined in only one individual of each species. An attempt was made to determine whether the number and size of glomeruli in fishes of the same species varied according to the size of the fish. In one series of eight

AGE, Aver- Maxi- Mini- Aver- Maxi- Mini- ’IR OENT age mum mum age mum mum

38.5 42 35 32.4 35 27 15.8 65.4 73 57 57.6 70 35 11.9 96.4 128 76 79.9 93 57 17.1

TABLE 1

ReZative shrinkage of large and small glomeruli in sectioning. (Sections fixed in Bouin’s, stained with H . and E . )

BODY Diameter, fresh SPECIES

Diameter, in sections

Teuthis hepatus Epinephelus striatus Ameiurus iiebulosus

goldfish of various body weights the number of glomeruli was counted (by the fractional method), the right and left kidneys being counted separately in each case. It was found that the right and left kidneys differed in the number of glomeruli by nearly 100 per cent in some cases, and neither side had constantly the greater number (table 2). Therefore, the infln- ence of body weight could only be examined on the basis of bilateral counts ; on that basis the lzumber of glomeruli varied directly with (but not proportional to) the body weight of the fish. An individual variation is indicated. The number was not more closely related to body weight than to surface area or vice versa.

To judge of the relation between body weight and the sige of the glomeruli, a second series of goldfish, six in number,

GLOMERULI I N THE KIDNEYS O F FISHES 429

BODY WEIQHT, QRANS BODY-SURFBCE AREA, SQ.CM.

was studied. After fixation by Bouin’s method, paraffin sections of the midportion of the posterior kidney were made. Ten glomeruli were measured in each case, and the average diameter was compared in the different individuals. The diameter was found to vary with the weight of the fish, although no definite proportionship is apparent (table 3) .

- AVERAQE OF F E N

QLOMERUlrI DIAMETER, MICRA

TABLE 2

Relation of body weight t o number of glomeruli in the goldfish

BODY WEXQRT, QRAXS

18.3 54.5 61 69.3 81.2 91.8

120 173 248

BODY-SURFACE AREA, SQ.CM.

62.6 128.6 139.5 152.1 168.9 183.2 219 279 355.1

NUMBER OF ffLOMERUIJ I N KIDNEYS

Right

4,964 2,718 4,932 4,251 2,742 7,700 7,274

13,622 15,623

Left I Both

3,307 2,944 3,952’ 6,741 4,940 6,048

10,240 6,943

Not counted

8,271 5,662 8,884

10,992 7,682

13,748 17,541 20,565

6.2 9.1

11.0 29.7 41.7

132.5

30.3 39.2 44.6 86.4

108.2 234

38.7 45.5 47.9 60.8 55.1 63.2

From the few individuals examined, it seems that the diameter varies quite directly as the body weight in small individuals, but is fairly constant for individuals of larger sizes, i.e., for those over 30 to 40 grams.

To study the amount of capillary branching within the glomeruli, fishes were injected with 2 per cent India-ink solution in normal saline. . This was found to delineate the capil-

430 JOSEPH NASH

laries more sharply than the Prussian blue, although the lat- ter was sometimes satisfactory for the purpose. The kidney was macerated as usual, and teased glomeruli were transferred by means of a fine pipette to a glass slide for examination under the high-power microscope. Camera-lucida drawings were made of these injected tufts.

RESULTS

The number of glomeruli found in one kidney of each species examined is given in table 4. It was at first assumed that the two kidneys of a given fish contained approximately equal numbers of glomeruli. The two kidneys are more or less fused into one median structure in most fishes, and for that reason their separation requires an artificial dissection. This is true of every species of fish encountered in this study, excepting the skate and hagfish, in which the kidneys are dis- crete. In many instances the fused kidneys were separated with the scalpel in the midline as accurately as possible, and a separate count was made of one or both kidneys. In all such unirenal counts the side to which the kidney belonged is indicated. In all other cases the right and left kidneys were counted together, and half the total thus found is given as the number of glomeruli in one kidney. I n comparing the glomerular content of the right and left kidneys, the artificial nature of their separation must be considered. I n the teleosts the anterior part of the kidney is composed mainly, and in many cases exclusively, of lymphoid tissue containing few, if any, glomeruli. In a few instances in which it contained glomeruli, this anterior part was counted separately, as indicated by the table.

In table 4 the number of glomeruli per kilogram of body weight and the number per square centimeter of body surface are calculated in each case. The body surface is calculated according to the formula of Rubner ( '24) :

Area (in sq. cm.) = K. q g where IC is a constant, 9 in the case of fishes, and g is the body weight in grams. This formula is not appropriate for

s

GLOMERULI IN THE KIDNEYS O F FISHES 431

such unfishlike forms as the eel, skate, and hfyxine, and its application to these is only a rough approximation.

For convenient reference the average diameter of the glomeruli in each species is included in the table. These measurements were made from sections by Dr. E. K. Marshall, Jr. The average diameter was at first taken as a rough index of the total filtration surface of the capillaries forming the intraglomerular tuft. However, as suggested by Marshall, it is more probable that the capillary filtration surface is proportional to the volume of the tuft, and therefore is more accurately indicated by the volume of the glomerulus than by its diameter. Considering the glomerulus as a sphere, its volume is proportional to the cube of the radius (r3). The significance of the diameter and hence of r3 is only relative; for the diameter was not measured in the same kidneys that were counted, but was determined in other individuals without regard to body weight and by a method (sections) known to involve an error. When r3, representing the relative volume of a glomerulus in cubic micra, is multiplied by the number of glomeruli in one kidney per square centimeter of body surface, the product indicates the relative volume of glomeruli in one kidney for each square centimeter of body surface. This figure reduced to cubic millimeters of glomeruli per square meter of body surface is included in the table as a relative measure of the total filtration surface in the different species.

All the glomeruli in the right kidney of Myxine no, 2 were measured fresh. The average measurements of the thirty- nine glomeruli were 673 x 581 ~.r, the largest being 1020 X 800 p and the smallest, 275 x 220 ~.r. These measurements agree approximately with those of Cone1 ( '17), when a difference of 15 per cent between the fresh and fixed tissue is allowed for. Maceration was unnecessary in the case of Myxine. Ureteral injection of Prussian blue was as efficient as arterial injection for counting. In one Myxine kidney instances were found of more or less union of two glomeruli, forming contiguous, confluent, and fused types. A conflu-

ZEP

c

lODY WEIGHT, QRAMS

WEIGHT OF ONE KIDNEY, GRAMS

NUMBER OF GLOMERULI IN ONE KIDNEY

NUMBER OF GLOMERULI IN ONE KIDNEY PEB KILO BODY WEIQRT

BODYSURFACEAmA, SQ.CM.

~~ ~-

NUMBER OF GLOMERULI IN ONE KIDNEY PEE SQ.CM. BODY SUEFAOE

AVERAGE DIAMETER OF GLOOMEEUIA, NICRA

RELATIVE VOLUME OF GLOMIRULI PER SQ. METER BODY SUR,FACE : CU.MM.'

31,5

56

37,9

15

149,

333

85.6

12

. Spa

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1151

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434 JOSEPH NASH

ent glomerulus had one bilobed Bowman’s capsule, containing two capillary tufts, connected with two tubules. A fused glomerulus had a less distinctly bilobed capsule connected with two tubules and contained only one capillary loop. One large glomerulus having only one tubule seemed to have two afferent and two efferent vessels.

The ramifications of the capillary could be followed more clearly when incompletely injected than when completely injected. I n a comparison of different species it seemed to be true that the larger the glomerulus, the more numerous were the branchings of its capillary. This general impression is based on examination of many partially injected tufts, a few of which are represented in plate 1. Unfortunately, the actual number of branchings cannot be determined from such partial injections. I n the eel many glomeruli contained two, three, o r four tufts, each apparently separate and distinct, the capsule being oval and unilocular as a rule; however, many multilobed capsules (two to four lobes) were found. In the bowfin a few, and in the wrymouth many bilobed Bow- man’s capsules were found (pl. 2). A very exceptional form of double glomerulus, found only once (in the skate), is shown in plate 2, fig. 3.

Camera-lucida drawings of a complete tubule of nineteen species are presented in plates 3, 4, and 5. A nearly complete skate tubule is shown in plate 6. Scale measurements of these tubules are given in table 5, showing the length and the approximate minimum and maximum diameters in each case. In a few instances two tubules were measured in the same individual. A more or less distinct constriction was recog- nizable just proximal to the glomerulus in many cases. Its approximate length is given, but the change of diameter at the neck was generally gradual, not abrupt. The measurements, of course, involve an error due to swelling of the tissues in the course of preparation and to flexions of the tubules in a vertical plane not represented in the flat drawing.

The glomerular diameter (from sections) for each species is included in table 5 . Although no proportion between the


length of the tubule and the diameter of the glomerulus is indicated, this point cannot be decided without measurements controlled as to body weight of the fish, shrinkage or swell-

TABLE 5

Heasurements of a complete kidney tubule in various species of fishes

SPECIES

Marine fishes : Pseudoscarus guacamia

(Cuvier) Gadus callarias Melanogrammus aeglifiiius Pseudopleuroiiectes

americaiius Pseudopleuroiiectes

americanus Mugil eurema Cryptacaiithodes maculatus Acanthurus hepatus Epiiiephelus guttatus Epiiiephelus guttatus Ocyurus chrysurus Myoxocephalus

ectodecimspiiiosis Myoxocephalus

ectodecimspiiiosis Epinephelus striatus Raja stabulaforis Myxine glutiiiosa

Fresh-water fishes: Perca flavesceiis Plecostomus commersoni Cypriiius carpio Carassius auratus Carassius auratus Amia ealva Anguilla rostrata Arytuilla rostrata

~

3ENQTH OF

PUBULE MM.

~

1.65 1.95 2.9

3.9

6.0 4.5 4.6 4.95 5.0 5.3 6.8

8.1

9.7 9.5

90.0 0.8

2.3 2.75 3.2 3.35 4.2 4.3 4.6 6.15

~

DIAM- CTER OF 'UBULE MICRA

30-50 40-70 40-60

50-80

40-85 50-90 40-60 25-60 30-60 30-60 30-70

50-80

40-80 40-70 50-15( 25-10(

30-50 25-70 30-80 30-70 30-80 25-90 30-80 30-80

IURFAC& AREA OF

ONE PUBULE, 8Q.MM.

2 0 7 .337 .455

3 0 8

1.134 .991 .723 .658 .700 .742

1.068

1.653

1.825 1.642

28.250 .155

.289

.413

.554

.526

.727

.783

.796 1.064

SQ.MM. 'UBULAI URFACI PEE

8Q.CM. BODY

IURFACI

4.97 8.09

12.12

17.00 41.63

5.28 30.90 24.5 26.0 18.6

18.2

20.1 37.4 28.25 0.232

47.5 64.0 39.9 22.1 30.5 32.9 18.3 24.5

rENQTH P NECE MICRA

__.

20 50 0

90

0 90

0 0 0

50

50 30

0 100

30 100 100 20 10

.~

DIAM- ETER OF fLOMER- ULUS (SEC-

TIONS) , MICRA

34 37 38

50

50 49 94 27 46 46 38

81

81 57

190 500

120 73 82 62 62 82

104 104

ing in preparation, and variations in length of different tubules in the same kidney. From the drawings the surface area of the tubule was calculated (length X 2nr). When this is

436 JOSEPH NASH

multiplied by the number of tubules in the kidney, the product represents the total tubular surface in the kidney. The measured tubule is assumed to be an average one in size, and the number of tubules in the kidney is taken to be the same as the number of glomeruli, inasmuch as no ‘blind’ tubules were found in these species. The tubular surface per unit of body surface in the different species is compared in the table.

A search was made for blind (aglomerular) tubules in every species mentioned in the tables. I n spite of a quite extensive search, none was found. In the sculpin three or four hollow clubbed endings were found in each kidney (pl. 2, fig. 4), but they appeared to be diverticula with dilated extremities rather than tubules. Their connection with the collecting ducts was not seen. The nearest approach to a blind tubule was seen in the flounder, a short straight diver- ticulum of a collecting duct (pl. 2, fig. 5). I n many species angular dilatations of the ducts were seen, most numerous in the goldfish, consisting of a bulging of the outer wall at a point of curvature of the duct. Blind endings of tubules are not detected with certainty by the maceration method, and failure to find them does not disprove their presence conclusively.

DISCUSSION

From a knowledge of the number of glomeruli in one or two individuals of a species, one does not know what variations in number occur within that species or whether such variations are related to age, to sex, to body weight, to surface area, or to other factors. This limitation is conspicuous in the case of fishes, for fishes have no fixed ‘normal’ adult size as have most other animals. Fishes of the same age may differ enormously in size, and also the size ultimately attained by each may differ greatly. No attempt is made in this study to determine the influence of age and sex on the number or size of glomeruli.

The average size of a few glomeruli in the kidney of one individual of a species cannot be considered an accurate average size for all the glomeruli in that one kidney, much less

GLOMERULI IN THE KIDNEYS OF FISHES 437

for the species as a whole. Therefore, in calculations of the volume of glomeruli in the kidney of a given individual, a serious error is probably introduced by the use of an ‘average’ glomerular diameter for a species.

In comparing different species as to ‘glomerular development,’ the volume of glomeruli (assumed to be a measure of filtration surface) per uait of body surface area is used as a basis of comparison. Possibly a comparison on the basis of body weight would be just as appropriate. A fairly sharp dis- tinction between fresh-water and marine teleostomi as to glomerular development is indicated. With the findings expressed in cubic millimeters of glomeruli per square meter of body surface, in seven out of eight fresh-water2 species the figure is above 10,000, above 25,000 in five of them; where- as in twenty-one out of twenty-four marine species the figure is below 10,000, below 5000 in eighteen of them. Some (marine) elasmobranchs and Myxine, with figures over 10,000, resemble the fresh-water teleostomi. If the capillary branchings are more profuse the larger the glomerulus, as they seem to be, the actual differences in filtration surface for marine and fresh-water teleosts are probably greater than these figures indicate. This relatively good glomerular development of fresh-water teleosts as compared to marine ones agrees with the hypothesis of the relationship of glomerular development to habitat proposed by Smith (’30) and developed by Marshall and Smith ( ’30).

Among the different species within a single family of teleosts an indicated difference in glomerular development of over 100 per cent is noted in the case of Teuthidae. In no instance is so wide a difference found among individuals within a single species, the greatest variation being noted in Balistidae.

No special study was made of tubular development, but from the estimations made (table 5), no marked difference between the fresh-water and marine fishes in this regard is

The catadromous eel, Anguilla rostrata, is arbitrarily included in the fresh- water group.

438 JOSEPH NASH

indicated. It is true, however, that the lowest values are found among the marine forms and the highest among the fresh-water forms, just as in the case of glomerular development. (Plecostomus, in which the highest tubular development is indicated, has an unusually long intestinal tract.) Tubules in the same kidney vary in length, and the one or two tubules measured may be far from the average size for the whole kidney. Furthermore, the size of the tubule probably depends to a great extent upon the body weight of the individual to which it belongs. In view of these facts and in view of the error due to swelling of the tissues during maceration, no conclusions as to relative tubular development can be drawn from the few uncontrolled data available.

In the Serranidae (pl. 3, red hind; pl. 4, grouper) a definite sharp transverse line was seen a short distance proximal to the glomerulus, as shown in the drawings, at which the epi- thelium changed suddenly from a clear translucent type fol- lowing the glomerulus to a darker stippled quite opaque type more distant from the glomerulus. This suggests that the stippled part is the brush-border segment and that another similar segment occurs immediately after the glomerulus and its neck. A careful investigation by the use of sections must be made to clear up this point.

SUMMARY AND CONCLUSIONS

1. Fractional and in many cases complete counts of the number of glomeruli were made on the kidneys of cyclostomes, elasmobranchs, marine teleosts, fresh-water teleosts, and ganoids. Glomerular development is generally much greater in the fresh-water teleosts than in the marine ones. The elasmobranchs and cyclostomes investigated resemble the fresh-water teleosts in having good glomerular development.

2. Studies of 'the capillary branching in the glomerular tuft were made of many species by means of injection and maceration technique. The branchings of the capillary tuft seem to be more numerous, the larger the glomerulus.


3. Measurements and drawings of a complete renal tubule are given, from nineteen species of fish. Tubular surface areas estimated from these figures do not seem to vary in different groups as does glomerular surface.

I am gratefully indebted to Dr. E. K. Marshall, Jr., for sug- gesting this study and for indispensable guidance and help throughout the work. Part of the work was done at the Mount Desert Island Biological Laboratory, Salisbury Cove, Maine, on species from near-by waters supplied by that laboratory. The work on tropical fishes was done at the Bermuda Government Aquarium, Flatts Village, Bermuda. I am grateful to Mr. L. L. Mowbray, curator of the Aquarium, for a pIentifu1 supply of material, for the identification of the tropical fishes investigated, and for the use of a laboratory during my stay in Bermuda. Mr. Louis L. Mowbray, Jr., assistant curator, and Mr. Roy Taylor, of the Aquarium staff, zealously aided in furnishing material. To Mr. Charles M. Breder, of the New York Aquarium, I am deeply indebted for much material, and for the identification of the same. I wish particularly to thank Dr. Homer W. Smith for his help and‘ for his kindness in making available to me the material and facilities at Mount Desert Island and at Bermuda.

BIBLIOGRAPHY AUDIGE, J. 1910 Contribution B 1’Btude des reins des poissons t6lBostBens. Arch.

2001. exp. et gBn., 5th ser., T. 4, p. 275. CONEL, J. L. 1917 The urogenital system of myxinoids. Jour. Morph., vol. 29,

p. 75. EDWARDS, J. G. 1928 Studies on aglomerular and glomerular kidneys. Am.

MARSHALL, E. K., JR. A comparison of the function of the glomerular

MARSHALL, E. K., JR., AND H. W. SMITH The glomerular development Biol. Bull., vol. 59,

RUBNER, M. 1924 Aus dem Leben des Kaltbluters. Teil 1. Die Fische. Bioch.

SMITE, H. W. The absorption and excretion of water and salts by marine

VINTRUP, BJ. On the number, shape, structure, and surface area of the Am. Jour. Anat.,

Jour. Anat., vol. 43, p. 75.

and aglomerular kidney. Amer. Jour. Physiol., vol. 94, p. 1.

of the vertebrate kidney in relation to habitat.

1930

1930

pp. 155-153.

Zeitsch., Bd. 148, S. 222. 1930

teleosts. 1928

glomeruli in the kidneys of man and mammals. vol. 41, p. 123.

Am. Jour. Physiol., vol. 93, p. 480.

GLOMERULI IN THE KIDNEYS OF FISHES PLATE 1 JOSEPH NASH

HADDOCK

SCULPIN

FlOUNDER WRY MOU TH

\ '- SKATE

MYXINE Camera-lucida drawings of partially injected glomeruli of different species of

fishes, indicating that the capillary branchings are more numerous the larger the glomerulus. (Common names in this and all the other plates correspond t o the same species mentioned in tables 4 and 5.)

440

GLOMERULI I N THE KIDNEYS OF FISHES JOSEPH NASH

R 1

PLATE 2

2

4 5 - +O.Srn- 4

Camera-lucida drawings. Double glomeruli: 1, amia; 2, wrymouth (injected) ; Blind diverticula of 3, skate (R. stabulaforis), an unusual form seen only once.

kidney tubules or ducts: 4, sculpin; 5 , flounder.

441

THE MIERICAN JOUBNAL O F ANATOMY, VOL. 47, NO, 2

GLOMERULI IN THE KIDNEYS OF FISHES JOSEPH NASH

PLATE 3

Camera-lucida drawings of complete kidney tubules. 1, perch; 2, parrot fish; 3, cod; 4, brown tang; 5, yellow tail; 6 and 7, goldfish; 8, flounder; 9 and 10, red hind

442

GLOMERULI I N THE KIDNEYS OF FISHES JOSEPH NASH

2

PLATE 4

- -0 .5mm -

Camera-lucida drawings of complete kidney tubules. 1, mullet ; 2, haddock; 3, grouper; 4, flounder; 5, eel; 6, carp; 7, loricaria; 8, amia.

443

QLOMERULI I N THE KIDNEYS OF FISHES J O S X P l I NASH

PLATE 5

Camera-lucida drawings of complete kidney tubules. 1 and 2, sculpin; 3, wrymouth; 4, eel; 5 , hagfish.

444

GLOMERULI IN THE KIDNEYS OF FISHES JOSEPH NASH

PLATE 6

Camera-lueida drawing of a nearly complete kidney tubule of skate (Raia stabulaforis) .

445

the number and size of glomeruli in the kidneys of fishes, with observations on the morphology of...

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