Naturalist 



itv between kinesodic and a^sthesodic cells prevail in the 

 Monocondylia. Whether we regard the brain of a fish as the 



conceded that the cells corresponding to kinesodic and 

 ;c-thcso(lic processes must be in .-ill probability represented. 

 The absence of the cortex limits our search to the axial lobe. 

 Observations upon various groups of reptiles have led me on 

 several different occasions to suggest that the axial lobe, seen 

 in those groups where the cortex is present, is a sort of pro- 

 liferating centre from which cortical cells are formed. l 



This hypothesis has been further substantiated by the obser- 

 vations of Mr. Turner, 2 upon the axial lobe of various birds. 

 It is also worthy of note that the birds resemble fishes in the 



therefore in the form of niduli within the axial lobe. It would, 

 therefore, appear legitimate to consider the axial lobe as the 

 source from which the cortex has sprung, so far as its histological 

 elements are concerned, a suggestion which is further empha- 

 sized by the fact, brought out by Professor His and extended 

 by the writer, that all neural elements arc derived from the 

 epithelial structures lining the ventricle. 



A corollary of this would be the concentration of all com- 

 missures and tracts belonuin- -trietlv to the cortex in the axial 

 lobe. The position of such structures might then serve to 

 determine the direction in which the complicated brain of 



1 Notes on the Brain of the Alligator. Journ. Cincinnati Society of Natural His- 

 tory, vol. XII, p. 455; Contributions to the Comparative Morphology of the Central 

 Nervous System, II. Morphology and Histology of the Brain of certain Reptiles, 

 Journal of Comparative Neurology, vol. I. p. 21, March 1891. 

 2 Journ. Comp. Neurology. Vol. i,p. yi. 



