350 JouRNAi. OF Comparative Neurology. 



the major divisions of vertebrates, has striven to show that 

 there is a constant difference in form between the kinesodic 

 and aethesodic cells. On this basis areas are marked off more 

 or less distinctively associated with one or the other function. 

 It was noted that the two kinds of cells are more distinctly 

 segregated in lower vertebrates, while in higher types there 

 is a greater tendency to inter-blend and form complex clus- 

 ters. In other words, there is a very obvious anatomical 

 basis for the assumption of more complex inter-action be- 

 tween afferent and efferent excitements in the cortex of 

 higher vertebrates. 



If the fish is not purely reflex and automatic in its re- 

 actions, some substitute for the undeveloped cortex must be 

 found, and would be sought for in the only remaining part 

 of the cerebrum, i.e., the axial lobe. As we have seen, the 

 axial lobe of Sauropsida is certainly much more than the 

 homologue of the striatum of mammals. The writer en- 

 deavored to show that in alligator and other reptiles there 

 are definite proliferating areas, which may be regarded as 

 centres of origin for the cortical niduli.(') Mr. Turner has 

 observed the same appearance in birds, (-) and his studies 

 make it probable that in that group, where the cortex is 

 greatly reduced, its loss is substituted for by involuted cell 

 niduli of cortical origin, but buried within the axial lobe. 

 This forms an important clue in the search for the homo- 

 logues of sensory and motor areas in the fish. 



In general, then, we believe that the fish cerebrum is 

 derived from a primitive type in which the primary prosen- 

 cephalic vesicle had scarcely, if at all, developed lateral (or 

 definitely cerebral) structures; that most teleosts have arisen 

 from types which possessed a slightly developed cortex, but 

 that an increase in the size of the head without the commen- 



1 "Notes on the Brain of the Alligator," Journ. Cin. Soc. Nat. Hist., Vol. XII, p. 

 455; " Topography and Histology of the Brain of Certain Reptiles," Journal of Com- 

 parative Nei-rologv, Vol. I, p. 21. 



2 C. H. Turner, " Morphology of the Avian Brain," Journal of Comparative 

 Neurology, Vol. I, p. 71. 



