HYPOPHYSIS OF PETEOMYZON AND AMIA 283 



situated in the nasal capsule described by Scott (1888). This 

 organ has been studied and is being described by me else- 

 where. It develops in close connexion with the olfactory organ 

 and has no histological or topographical similarities with the 

 pars tuberalis of other forms. 



In the description of its origin in other forms the pars tuberalis 

 arises as lateral processes (lobuli laterales) which develop 

 acini composed of chromophobe cells, and which are closely 

 adpressed to the brain. According to Tilney it arises in con 

 nexion with the pars intermedia (his pars infundibularis). 

 If the pars tuberahs is represented at all in Petromyzon, 

 I suggest that it is the ' Uebergangsteil '. Its cells are chromo- 

 phobe (Herring, 1910), it has lateral extensions which are closely 

 adpressed to the brain-wall, and is the only part of the organ 

 not otherwise accounted for. From its position between the 

 pars anterior and the pars intermedia it can hardly be said to 

 arise in connexion with the one rather than with the other, 

 though Sterzi considers it to be more closely related to the 

 pars intermdia. 



II. Ami A CALVA. 

 Introduction. 



The hypophysis of Amia calva is described by Dean 

 (1896) as developing late. He regarded it as ectodermal, 

 though he admitted that its ventral limit could not be distin- 

 guished from the endodermal roof of the fore-gut. 



Subsequently Prather (1900) investigated the question and 

 concluded that the hypophysis of Amia w^as of endodermal 

 origin and derived from the roof of the fore-gut. 



Later still, Keighard and Mast (1908), as a result of their 

 researches, believe that Prather was misled in his conclusions 

 by artifacts in his preparations due to shrinking, and they 

 claim that the hypophysis of Amia arises from the ectoderm 

 close to the neuropore, dorsal to and separate from the 

 stomodaeum. 



Smith (1914) regards the hypophysis as of ectodermal origin, 

 but thinks that endoderm cells are contributed to it. 



