Eycleshymer- Davis, Epiphysis and Parapliysis in Amia. 59 



etal-pineal eye of the Cyclostomata and other vertebrates has 

 been developed from a median portion of the pigmented eye of 

 Amphioxus. The rudiments of the eye were derived from 

 (segmental) sense organs, but the eye itself is never developed 

 from two right and left halves, in so far as the closure of the 

 medullary folds would necessitate this." 



Petromyzon is the only form among the Cyclostomes in 

 which the early history of the epiphysial structures has been 

 traced. In the adult, Ahlborn discovered two epiphysial ves- 

 icles, and from their position called them the superior and infer- 

 ior. Dohrn, Balfour, Scott, Owsiannikow and others showed 

 that the superior arises at about the time of hatching (3-4 mm. 

 larva) as an evagination of the roof of the thalamencephalon. 

 These investigators found that the inferior vesicle did not ap- 

 pear until the larva had reached a very late stage (17-26 mm.). 

 Whether the inferior vesicle was an outgrowth from the supe- 

 rior, or arose from an independent source was not known until 

 Kupffer clearly showed its mode of origin. The author found 

 the superior to arise at the time and in the manner described 

 by the above named investigators. The inferior however arises 

 in a 5 mm. larva as an evagination in the posterior portion of 

 the roof of the prosencephalon. This structure grows back- 

 ward and its distal end enlarges to form the inferior vesicle 

 of Ahlborn. To this structure Kupffer gives the name "sec- 

 ond epiphysis" and believes it to be directly homologous with 

 the paraphysis of Amphibia. 



Studnicka, in a publication prior to that of Kupffer, found the 

 superior to arise as described by previous authors. He de- 

 scribed certain stages in the development of the " parapineal 

 organ" ("inferior vesicle", "second epiphysis ") and believes, 

 although he did not observe the early stages of development, 

 that this organ arises from the roof of the thalamencephalon in 

 front of the superior commissure and not from the prosencepha- 

 lon as stated by Kupffer. Studnicka maintains that there is a 

 third outgrowth from the roof of the prosencephalon which 

 corresponds to the paraphysis of other forms. 



According to all authorities these two organs are highly 

 nervous. Studnicka found the superior vesicle to be attached to 



