400 EYCLESHYMER. [Vol. X. 



tact with the superficial layer of the epiblast is but a single 

 layer. The nuclei undergo a marked migration toward the 

 periphery, and in this respect the appearance is strikingly 

 similar to the condition found in the optic vesicles, which at 

 this time are strongly evaginated. The presence of pigment 

 at the inner ends of the cells is also a significant fact. 



From this time until the formation of the lens in the lateral 

 eye, the epiphysis increases in size, its cavity becomes ellipti- 

 cal and is in wide communication with the thalamocoele. 



At the time of the invagination of the lens there appears in 

 the posterior portion of the roof of the prosencephalon a sec- 

 ond median outgrowth which is probably homologous with the 

 paraphysis described in Reptilia by Selenka. 



In a 12 mm. larva the paraphysis is much elongated; lateral 

 diverticula appear at its distal end while the cavity is obliter- 

 ated proximally in a manner analogous to that which occurs in 

 the epiphysis. The changes are more pronounced in 14 mm. 

 larva where it has assumed a digitate appearance and bears 

 a striking resemblance to the true choroid plexus of the lateral 

 ventricles. Hill ('94) has described the paraphysis in Amia 

 and believes that it likewise later forms a part of the choroid 

 plexus. 



The two structures in Urodela never come into close rela- 

 tion, as in Reptilia, but remain widely separated. That the 

 paraphysis is indeed a peculiar organ, very similar in develop- 

 ment to the epiphysis, is shown not only by Selenka but 

 also by Leydig in his final memoirs, where from its exceptional 

 mode of development, the name "anterior epiphysis" is sug- 

 gested. The hypothesis of Selenka that it is a degenerate sense 

 organ, is certainly questionable; much more that its ancestral 

 function was audition. 



The variation in the point of origin of the paraphysis, and its 

 formation at a much later period than the epiphysis, would 

 seem to indicate a less important ancestral function. The 

 phylogenetic importance of the epiphysis is certainly indi- 

 cated by the fact that it is formed at a fixed point through- 

 out the vertebrate phylum. While it must be admitted that we 

 are without evidence sufficient to warrant us in making any 



