viii Journal of Comparative Neurology. 



shows that this character is too variable and too liable to convergence 

 to have any very wide application in this direction. 



The remarkable forms assumed by the optic nerves of fishes are 

 striking illustrations of the amount of variation possible in a very 

 simple structure under varying conditions, the decisive factor in this 

 case being probably the necessity for the proper nourishment of the 

 nerve in large-eyed species. 



Another interesting point brought out in this connection is the 

 fact that the parietal nerve in Ammocoetes develops the same as the 

 optic, as a tubular outgrowth into which fibers grow from the retina 

 and the original cells of the tube are, as before, crowded into an axial 

 strand and transformed into glia cells. It is very interesting that a 

 nerve so little differentiated as the nerve of the pineal organ can be 

 divided into several parallel strands in the course of its development. 



C. J. H. 



The Cerebral Fissures of the Lemurs.^ 



Professor Ziehen continues his studies of the surface anatomy of 

 the cerebrum. Having already devoted considerable attention to com- 

 parisons between the fissures of the primates and various carnivora 

 and allied types, the chief interest in this study centres about the ques- 

 tion of the relations of the prosimian to these two types of fissures. 

 The result of a detailed comparison is the conclusion that while the 

 lemurine fissuration is directly comparable to the carnivore type (this 

 is illustrated in a comparative table), yet it is nearer to that of the pri- 

 mates. In fact, the prosimian type is to be regarded as the prototype 

 or fore-runner of the primate, but not as an intermediate stage be- 

 tween the latter and the carnivore. The carnivora and the primates 

 exhibit a common fissural plan, which has, however, been independ- 

 ently elaborated in the two cases. Within the Prosimia, however, we 

 find no evidence of more than one phylum. On the other hand the 

 comparative anatomy of the cerebral surface shows a unity of struc- 

 ture which cannot be explained by convergence. We must refer the 

 reader to the figures and tables of the author for the data on which 

 these conclusions are based. c. j. h. 



' Ziehen, Th. Ueber die Grosshirnfurschung der Halbaffen urid die Deu» 

 tung einiger Furchungen des Menschlichen Gehirns. Archiv f. Fsychiatrif, 

 XXVIII, 3. 



