SCIENCE. 



253 



mitted to absolute alcohol for a day before entire 

 removal from the skull, then put in a mixture of 

 methyl-alcohol and bichromate of potash, of a 

 muddy beer color (thirty grains of the salt to the 

 ounce of alcohol ) for a week, and subsequently, for 

 a variable time according as the specimen will 

 harden, to simple Midler's fluid. The staining, 

 cutting and mounting can be done exactly as in the 

 former case. 



Specimens prepared by the first method of har- 

 dening will furnish better results for the medulla, 

 those hardened with the second will yield more 

 complete specimens of the higher ganglia. It is a 

 well known fact that fluids that will harden the 

 medulla oblongata well will sometimes fail to 

 render the cerebrum and mesencephalon fit for 

 cutting. 



Of course the most important series of sections 

 will be one taken transversely to the peduncular 

 axis. This should be made first, therefore, and 

 studied in conjunction with the delineations made 

 from the coarse specimens. Now the student hav- 

 ing familiarized himself with the precise topo- 

 graphy and extent of every ganglion, cortical ex- 

 panse and fibre mass, is ready to proceed to more 

 complicated inquiries, that is to study the relations 

 of fibre masses. How he may proceed where a 

 fasciculus does not run in a straight plane, I have 

 indicated in a previous contribution to this journal.* 



It is needless to say that in addition to these 

 methods, which may be called systemic ones, inas- 

 much as they are calculated to reveal homologies 

 and relations, that all other methods of hardening 

 and staining may be used to study the finer and 

 finest histology. They are of less importance, 

 however, both to the zootomist and neurologist, 

 than is generally supposed. 



Now a word as to the objects of such an inquiry, 

 for unless the investigator has a definite point in 

 view, and a provisional notion of the subject he 

 intends to develop, his work will be barren of result, 

 save he stumble on some revelation accidentally. 



a. The close relation between the cerebral lobes 

 and the olfactory lobes of fishes may, if studied in 

 all the groups, particularly the lampreys, lead to 

 the establishment of a homology with the so-called 

 cerebral lobes of the higher invertebrates. 



b. The fact, which we have every reason to sus- 

 pect to be a fact, that the cerebral lobes of fishes 

 are the true homologues of the cerebral hemis- 

 pheres of the mammalia, sauropsida and amphibia, 

 requires to be definitely established. Prof. Burt G. 

 Wilder questions this homology, on the ground that 

 the cerebral lobes of bony fishes are solid, and con- 

 tain no ventricles. That so acute an observer, one 

 to whom we owe so much in the line of correction 

 of gross errors which have found their way into 

 standard text books, could lean his objection on 

 such a doubtful basis, shows how catholic must 

 become the principles, if I may so term them, of 

 cerebral anatomy. The embryological develop- 

 ment of the fish's brain presents features which no 

 other vertebrate brain exhibits in the course of de- 



* Part I. of this series, Journal 0/ Nervous and Mental Disease, 

 1887, p. 668. 



velopment, namely, the entire central nervous axis 

 is apparently solid. In truth it is hollow, but the 

 cavity is a mere slit, the walls of which are in con- 

 tact, and when the cerebral lobes become solid they 

 do so by the fusion of these walls and the oblitera- 

 tion of the slit. The ventricle is therefore not an 

 essential feature of the cerebral hemisphere, and as 

 if to prove this fact beyond a doubt, we find that 

 among animals as nearly related as sharks, some 

 have true ventricles in these lobes communicating 

 with the third ventricle, while others have them as 

 solid as the bony fish. 



c. The derivation of the olfactory bulb, a struc- 

 ture often and unwarrantably confounded with the 

 olfactory lobe, can be best studied in fishes. 



d. The same applies to the cerebral epiphysis 

 and hypophysis, still known by the improper titles 

 of pineal and pituitary glands. 



e. The relations of the peculiar lobi inferiores 

 to the optic nerve, and the asserted homology of 

 the corpora candicantea require confirmation. 



f. The question of the homology of the cerebel- 

 lum and optic lobes, which is in a very unsettled 

 state to-day, is yet unanswered. Wilder, in his 

 paper on the brain of the Chimcera, has exposed 

 the fallacious interpretations which most authors 

 have made in this regard. His essay will prove 

 valuable to those engaged in this inquiry. Possibly 

 the discovery by myself of the entire distinctness of 

 the post-optic and the hitherto unknown inter-optic 

 lobes in reptiles, from the optic lobes proper, may 

 assist in unraveling the true relations. 



g. Since among fishes we find many examples 

 of remarkable development of the periphery, I need 

 but instance the rostrum of Spatularia, the great 

 lateral expansions of the skate, the asymmetry of 

 the Flounder, the rudimentary eyes of Amblyopsis, 

 the inarsupium of the Hippocampus, and the im- 

 mense jaw of the Angler, an inquiry dealing with 

 the relations of nerve centres to the projected peri- 

 pheries may be expected to furnish many suggest- 

 ive facts bearing on the projection doctrine. 



All through these lines it will be seen that as in 

 every other branch of morphology a study of em- 

 bryonic development is an essential to a proper 

 knowledge of the fish's brain. A brief considera- 

 tion of the methods to be employed in this field of 

 the study will not be out of place. 



Spawn can be obtained living from our fish 

 hatching depots, whose superintendents will be 

 found very obliging towards those requiring mate- 

 rial for scientific study. The different stages of 

 development, extending to beyond the period when 

 the young fry escapes, can be obtained by permit- 

 ting the ova to develop under the eye of the ob- 

 server in a hatching trough. 



The ova of bony fishes are dropped into a solu- 

 tion of chromic acid, or Muller's fluid ; better, a 

 few specimens are taken out each day and dropped 

 each into differently strong solutions of the former 

 and into the latter. I know of no standard strength 

 that will yield uniform results, and have while 

 working in this field in Vienna lost thousands of 

 ova by following the routine directions. 



From the chromic acid and Muller's solutions the 

 spawn js transferred to, alcohol in from two to 



