i6o Journal of Comparative Neurology. 



brum may be equivalent to the mesal wall (callosal eminence) 

 in Diemyctyliis, in which case the membranous roof of the fish 

 cerebrum would represent the crumpled plexuses of higher 

 forms. This view has been endorsed by Studnicka. We might 

 then expect to find in ganoids a commissure exactly compara- 

 ble to that found in Amphibia. 



The projection of the terma into the aula noticed by Mrs. 

 Gage in Diemyctylus and Amia, to which she applied the term 

 crista, (a name given by Wilder ('80) to a similarly situated 

 object discovered by him in the mammalian brain) exists in 

 Ncctiiriis merely as a slight intrusion of the pia covered by 

 endyma. It is in this region that Herrick has figured fibers 

 which he considered a possible callosum. As before stated, I 

 fail to find any trace of such. 



DienccpJial. — This and the following segment are but 

 slightly differentiated from each other ectally. Upon the dor- 

 sum a slight transverse furrow dorsad of the postcommissure, 

 and the prominent caudal bend of the dorsal wall of the infun- 

 dibulum on the ventral aspect, may be regarded as boundaries. 

 Cephalad of the postcommissure, which may be considered as 

 limiting the caudal extent of the segment in the roof, the solid 

 walls of the diencephal become divaricated and the roof at the 

 meson is formed by the endyma and pia alone. This consists 

 of a single layer in its cephalic portion passing caudad into the 

 peculiar several-layered endymal structure ventrad of the post- 

 commissure, which has been described by Mrs. Gage ('93). At 

 the supracommissure the walls approach to separate yet more 

 widely cephalad of it, where the roof, diatela, is greatly ex- 

 panded, limited cephalad by the velum ; this is oblique, so that 

 a large sac is formed dorsad of it, extending also laterad at 

 each side cephalad of the habenas ; it is the postparapJiysis of 

 Herrick ('93, 2), by whom the /^r^/Zy^/jr is termed Xho. prepara- 

 physis. 



Epiphysis. — This in Nectunis consists of an aggregation of 

 closed vesicles, forming a flattened suboval body upon the dor- 

 sum of the brain between the post- and supracommissures. 

 Fig. 23 shows a transection of it. No connection with the dia- 



