Sorensen, Study of Epiphysis and Roof of Diencephalon. 41 



ka. Its walls consist of a single layer of cells, the outer ends 

 of which are pigmented. In larvae of 12 mm. the paraphysis 

 is much elongated and lateral diverticles appear at its distal end, 

 while the cavity is obliterated proximally in a manner analagous 

 to that which occurs in the epiphysis. The changes are more 

 pronounced in a larva of 14 mm., where the organ has assumed 

 a digitate appearance and bears a striking resemblance to the 

 true choroid plexus of the lateral ventricles. The two struct- 

 ures in Urodela never come into close relation, as in Reptilia, 

 but remain widely separated. Leydig suggests the term ' ' an- 

 terior epiphysis " for the paraphysis. The variation in the 

 point of orgin of the paraphysis and its formation at a much 

 later period than the epiphysis would seem to indicate a less im- 

 portant ancestral function. The phylogenetic importance of the 

 epiphysis is certainly indicated by the fact that it is formed at a 

 fixed point throughout the vertebrate phylum. Its ontogeny 

 indicates that it arose at a time when a neural canal was first 

 formed. If we admit the hypothesis, which I believe I have 

 proved in Amblystoma and Rana, that the lateral eyes are pres- 

 ent as a pair of depressions in the cephalic neural plate, we 

 might suggest that at the phylogenetic period when they became 

 implicated by the closing of the neural folds a median eye would 

 arise and become most highly functional during the period in 

 which the lateral eyes were non-functional or least functional. 

 This might explain its unpaired origin. 1 



Burckhardt (p-92) thought he had seen the pineal of Pro- 

 toperus, but states that he had only a part of the pineal before 

 him. He includes in the term tela choroidea superior, all the 

 ependymatic forms of the diencephalon lying in front of the 

 supra-commissure. Continuing his discussion he says : If we 

 now consider the roof of the diencephalon in a perpendicular 

 section, we find immediately in front of the post-commissure a 

 little short, stout, but not always naked, ependymatic portion, 



1 Compare with this suggestion the more recent articles of Locy (0/-'93 and 

 '94) and Prenant (70-9$). It is also interesting to note that in 1891 Professor 

 C. L. Herrick made the same suggestion in a special course of lectures on Neu- 

 rology delivered in the University of Cincinnati. 



