78 P RATHER. [VOL. I. 



endodermic in origin in Lepidosteus as well as in Amia, and I 

 venture the prediction that a further study of Acipenser will 

 demonstrate the same for that form. The foregut extends far 

 forwards in each of the Ganoids in which its development has 

 been studied, and the writer believes that in all these it arises 

 from the endoderm. A study of the figures of the head parts 

 in those animals in which the hypophysis is undoubtedly of 

 ectodermal origin shows that in them the foregut stops short 

 of the infundibulum, while in some, at least, of those forms in 

 which its origin is questionable --ectodermic or endodermic - 

 the foregut and stomodaeum meet at an intermediate point, 

 directly under the base of the thalamencephalon. These facts 

 lead me to suggest that mechanical factors, acting at the point 

 of fusion of the brain base to the oral roof, may play an impor- 

 tant part in determining its development from this or that 

 layer. 



If my observations be confirmed, that the hypophysis in 

 Amia is derived from the hypoblast, will this fact strengthen 

 Kupffer's hypothesis that it represents a degenerated " paleo- 

 stome," or will it rather revive the old theory of Dohrn, that it 

 represents a portion of a canal connecting the alimentary tract 

 with an exterior dorsal opening through the thalamencephalon 

 and the epiphysis and accordingly believed to be homologous 

 with the invertebrate pharynx ? I find nothing in its structure 

 or its relations, other than its point of origin, which can be 

 interpreted as evidence in support of either hypothesis. I have 

 given what I believe to be the facts, but must leave their inter- 

 pretation to the maturer judgment that will come from the more 

 complete and extended observations of the future. 



Ilri.i, ANATOMICAL LABORATORY, 

 September 22, 1899. 



