Volume IV. jFiify, iSgo. Number i. 



JOURNAL 



OF 



MORPHOLOGY 



THE ORIGIN OF THE CEREBRAL CORTEX AND 

 THE HOMOLOGIES OF THE OPTIC LOBE 

 LAYERS IN THE LOWER VERTEBRATES. 



By ISAAC NAKAGAWA, B.Sc, 

 Morphological Laboratory, Princeton College. 



Edinger's discovery of the cortical gray as distinct from the 

 ventricular gray in the Reptilia (i, p. in) leads naturally to the 

 supposition that the rudimentary cortex, if nothing more, must 

 be present in the amphibian cerebrum, in which the mantel is, 

 in its relative size at least, not so very different from that of the 

 reptiles.^ And if we are able to find the homologous structure 

 in Amphibia, what is the extent of that homology when we take 

 into comparison the air-breathing vertebrates as a whole t The 

 first part of this paper contains the result of my observations 

 along that line. The second part consists of investigations 

 directed to determining the homology, and in part the functions, 

 of the several layers described by Osborn and others in the 

 tectum opticum of Rana (2, p. ^2) in comparison with those of 

 the reptiles and birds. 



The researches have been made under the supervision of 

 Professor Osborn in the Class of 'yy, Biological Laboratory 

 of Princeton College. 



iThis is not admitted by Edinger (i, p. io8). "Das erste was an diesen 

 Schnitten auffalt, ist, dass keine Spur von einer Hirnrinde zu sehen ist." 



