524 p. E. SMITH 



THE DEVELOPMENT OF THE HYPOPHYSIS 



The literature shows a considerable diversity of opinion in 

 regard to the origin of the hypophysis. The three views held in 

 regard to its formation are: that it is of ectodermal origin, that it is 

 of entodermal origin, and that both ectoderm and entoderm enter 

 into its formation. The literature has been frequently reviewed. 

 Minot ('92), Kingsley and Thyng ('04) and Tilney ('11) each have 

 good reviews. 



The view that the hypophysis is ectodermal in origin has the 

 largest number of supporters, among whom some of the best 

 known are: Goette ('75) in Bombinator; Mihalkovics ('75) in the 

 goose, rabbit and dog; Kolliker ('79) in maimnals; Kraushaar 

 ('84) chiefly on Mus musculus; Hoffman ('86) in the bony fishes; 

 Scott ('87) in Petromyzon; Gaupp ('93) in Lacerta andAnguis; 

 Salzer ('87) in the pig and guinea-pig; Haller ('98) in a series of 

 forms; Minot ('98), Corning ('99) in Rana; Zeleny ('01) in chel- 

 onia (Aspidonectes, Chelydra, Chrysemys) ; Kingsley and Thyng 

 ('04) in Ambly stoma. 



Giving the hypophysis as ento-ectodermal in origin are Hoffman 

 ('86) in Reptilia; Gregory ('03) in Salmo alsaticus, S. salar, and 

 Esox; Kupffer ('94) in Rana; Valenti ('95), Nusbaum ('95) in the 

 dog. 



Prather ('00) in Amia finds the hypophysis to be entirely ento- 

 dermal. Kingsley and Thyng ('04) think that not early enough 

 stages were selected to show its real origin in this form. Tilney 

 ('11) gives a good review of the literature but adds nothing to the 

 embryology, the paper being chiefly on the comparative histology 

 of the gland. There seems to be a tendency among text-books to 

 consider the question as settled, and that the hypophysis is 

 entirely of ectodermal origin, but much of the work will have to be 

 confirmed before such a generalization will be warranted. 



In Desmognathus, T have found it difficult to determine with 

 certainty whether the entoderm contributed to the organ or not. 

 There is a very close association between the ectodermal hypo- 

 physial invagination and the pre-oral entoderm up to my Stage X, 

 when the separation becomes very definite. At times the relation 



