Resumen por el autor, Roy Lee iMoodie, University of Illinois.

ExBmen microsc6pico del cerebro de un pez f6sjl.

El exsmen microscGpico de secciones de un n6dulo que con- tenia el cerebro de un pequefio pez paleoniscido de las Coal Mes- ures de Kansas ha permitido determinar la existencia de un ancho espacio meningeo y la posible conservaci6n de las meninges y vasos sanguineos. El espacio meningeo estB ocupado por cal- cita vesicular que se separa ficilmente de la superficie del cere- 1x0, nervios y oido. La substancia cerebral estB convertida en cristales incompletos de calcita y fosfato.

Puesto que todos 10s n6dulos con cerebros conocidos hasta el presente son casi de la misma naturaleza y substancia, no ser j posible descubrir vestigios de estructuras neurales microsc6picas hasta que se encuentren cerebros fosilizados en un medio difer- ente. El hecho de que la forma del cerebro no se haya alterado puede explicarse por la naturaleza incompleta de 10s minlisculos cristales que reemplazaron a su substancia. La formaci6n de estos cristales ha borrado todo vestigio de la estructura orghjca, conservtindose tan solo la forma del cerebro. Esta sin embargo se ha conservado con una belleza que no ha sido nunca sobre- pasada en material fosilizado.

Translation by JOSE F. h'onldez Cornell Mcdiral College, New YOI k

AUTHOR’S ABGTRdCT OF THIS PAPER ISSUED

B Y T E E BIBLIOGRAPHIC SERVICE, OFPOBER 4

MICROSCOPIC EX;IMINBTION OF A FOSSIL FISH BRAIN

ROY 1,. hlOODIE

Department of Anatomy, Universi ty of I l l inois , Chicago

TWO FIGURES

When I published my first study ( I ) on the ganoid fish brains from the Coal Measures of Kansas I had no material which could be spared for sectioning, although I was extremely anxious to determine if there were microscopic evidences of organic structure in the petrified material. Since that paper appeared I have received through the kindness of my friend, Bennett Mills Allen of Kansas University, a series of nodules containing fish brains which he had collected at the quarry and brought to Chicago for me. Examination of all the specimens under the binocular showed no essential differences in external form of the brain from those previously described, so it was decided to devote one of the brain-containing nodules to sectioning, to find, if possible, traces of fiber paths or nuclei, or any organic structure which might be preserved.

Sections of an entire nodule with its contained brain, which had been slightly chipped to determine the presence of neural structures, were cut for me at the laboratories of the United States Geological Survey by Mr. F. S. Reed, with a thickness of about 12 microns. A favorable region is shown in the photomi- crograph (fig. 2) at a magnification of 70 diameters. Owing to the crystalline nature of the material it was not deemed neces- sary to attempt staining, since an examination of the results of Professor Lignier (2) who stained sections of fossil cycads with vesuvine (Bismark-brown, or tri-amido-azobenzene) and Seitz (3) who used an aqueous solution of Eosin, after a most elabo- rate technique of preparation of the fossil bones of dinosaurs and

329

330 ROY L. MOODIE

other fossil reptiles, has failed to convince me that there is any advantage in such a complicated method. Sections prepared by the petrographic method, which consists in cutting with a saw and grinding with emery powder on a leaden disc, are fully as

Fig. 1 Kentucky. line.

Brain of Rhadinichthys deani Eastman from the Mississippian of The plane of the section is shown in the heavy transverse X 10.

This brain is almost identical in type with those from Kansas.

useful, and so far as the photomicrographs show fully as capable of exhibiting anatomical detail as the more tedious methods of Lignier and Seitz. This statement is based on an examination of several score of sections of fossil structures, chiefly bone, rang- ing in age from the Devonian to Recent, all of which have been prepared by the petrographic method. In the present instance

FOSSIL FISH BRAIN 331

it was well that staining was not attempted, since there are no evidences whatever of organic structure; only the outer form of the brain, nerves and semicircular canals are preserved.

In attempting to solve the problem presented by the preserva- tion of these little fish brains I was at a losrj to explain the fate of the meningeal space which in most of the recent fishes is quite

Fig. 2 Photomicrograph of a section through a brain-containing nodule from the Coal Measures of Kansas. X 70. There are three important areas in this untouched photograph: I) A dark area running entirelyacross the picture a t the bottom, extending about, one-third of the distance up the right side, and running obliquely downwards to the left, representing the phosphate or substance of the nodule which has replaced the brain case. The upper surface of this substance then represents the floor of the brain case. 2 ) A lighter area composed of rounded irregular spaces representing the meningeal space which has been filled with calcite. 3 ) The substance of the brain itself, or a t least. a portion of the left cerebellar lobe, showing its structureless nature. This area is seen in the triangular portion cut off by a dark band in the upper right hand corner of the figure. The most important and only new thing established by this figure is the extent of the perineural space, which is seen to be quite large and is comparable to the meningeal spaces of modern fishes.

extensive. The meningeal spaces in the present fish brain are filled with masses of calcite crystals whioh are separated by threads of calcium phosphate. The phosph.atic threads may be the representatives of blood vessels but I doubt it since the same

332 ROY L. MOODIE

threads occur in the substance of the nodule itself and the brain substance is entirely free from such threads.

I have shown in figure 2 an enlargement of 70 diameters of a portion of the meningeal space. The dark band at the bottom of the figure is the substance of the nodule, through which the plane of section is indicated in figure 1 by the heavy transverse line cutting the optic lobes and the cerebellar lobes. The light area in the substance of the nodule is calcite, usually entirely crystalline; the dark areas represent the phosphate of calcium and are nearly opaque. On this darker areareposes the meningeal space filled with threads of phosphate and calcite crystals. In the upper right hand corner is a portion of the left cerebellar lobe, which in the photomicrograph appears structureless, but under the microscope and better under the polariscope the substance of the brain is seen to be converted into incomplete crystals of cal- cium carbonate (calcite) and calcium phosphate. The polari- scope shows this substance in a lighter blue than the n-ell-formed calcite crystals in the meningeal space. The transverse striae seen in these latter calcite crystals in the photomicrograph are the orthorhombic cleavage planes of the crystals.

It is suggested elsewhere (4) that the brain substance may have been converted into palmitate or cholesteryl stearate, which enabled it to retain its form until more adequate fossilization could set in. In the present instance, if this were true, it would also explain the preservation of the meningeal spaces which were filled x i th a calcium magma before true fossilization set in.

There are no traces whatever of either cartilage or bone. The brain case and skull have been completely transformed into cal- cium phosphate. If the phosphatic portion represents the brain case, and I have every reason to believe it does, then we have the interesting addition to our knowledge of Paleoneurology, and one which justifies the publication of this paper; that is, Carboniferous ganoid fishes of the paleoniscid type had a wide meningeal space as do most modern fishes. This meningeal space is filled with calcite crystals, separated by threads of phos- phate giving the substance a vesicular appearance to the naked eye or under low magnification.

FOSSIL FISH BRAIN 333

SUMMARY

Microscopic examination of sections through a nodule contain- ing the brain of a small paleoniscid fish from the Coal Measures of Kansas has resulted in the determination of a wide meningeal space, and the possible preservation of the meninges and blood vessels. The meningeal space is filled with vesicular calcite which is readily broken away from the surface of the brain, nerves and ear.

The brain substance itself is converted into incomplete crystals of calcite and phosphate. Since all known brain containing nodules are of about the same nature and substance it will not be possible to discover evidences of microscopic neural struc- tures until brains are found fossilized in a different medium. The fact that the form of the brain was not distorted is explained by the incomplete nature of the minute crystals which replaced its substance. The formation of these crystals has obliterated all traces of organic structure, and only the form of the brain is preserved. This, however, is retained in a beauty which has never been surpassed in fossilized material.

BIBLIOGRAPHY

(1) MOODIE, ROY L. 1915 A new fish brainfrom the Coal Measuresof Kansas, with a review of other fossil brains. Jour. Comp. Neurol., vol. 25, pp. 135-181, 19 figs.

(2) LIGNIER, 0. 1892 ’L’Emploi de la vesuvine dans 1’6tude de vegetaux fos- siles. Bull. SOC. Linneenne de Normandie, 4th ser., Caen, vol. 6 , pp. %lo.

(3) SEITZ, ADOLF LEO LUDWIG 1907 Vergleichenden Studien uber den mikro- skopischen knochenbau, etc., Nova Acta Abh. d. Kaiserl. Leop. Carol. Deutsch. Akad. d. Naturf., Bd. 87, no. 2.

Concerning the fossilization of blood corpuscles. Amer. Naturalist, vol. 54, pp. 460464, 1 fig.

(4) MOODIE, ROY L. 1920

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 32. NO. 3