504 REIGHARD—MAST. [Vor xe 
sis differs further from that of Amia in being continuous 
at its ventral end (in early stages) with the entoblast of the 
dorsal wall of the archenteron. The lumen of the tube opens 
at one end into the archenteron, while at the other end it is 
closed by the outer layer of ectoblast. In Amia we have not 
found the hypophysis at any time tubular, nor have we found 
any lumen until some time after the separation of the organ 
from the ectoblast. We have not at any time found a connec- 
tion of the hypophysis with the entoblast. 
The hypophysis of Amia is in close contact with the ento- 
blastic button, which in an earlier stage is the middle of that 
part of the archenteric entoblast designated in the preceding 
article as the crescent (Fig. 1). The plane of demarcation 
between the ectoblast of the hypophysis and the entoblast of 
the crescent or button is not always easy to find. Its visibility 
depends on the plane of section. In suitable sections we have 
always found it as shown in Fig. 1, and we believe that it 
always exists. In respect to these two points, the existence 
in it from the beginning of a lumen and the continuity of its 
walls with the entoblast, the hypophysis of Amia may be in a 
less primitive condition than that of Acipenser. 
It is not our purpose to discuss at length the theory ad- 
vanced by v. Kupffer, on the basis of his work on Acipenser 
and Petromyzon, to the effect that the hypophysis is a palzos- 
tome. The development of the organ as we have described 
it in Amia certainly adds force to the array of facts adduced 
by v. Kupffer in support of his theory. 
In this connection it should be noted that we know but three 
vertebrates in which the hypophysis originates in connection 
with or near the neuropore, Petromyzon, Acipenser and Amia. 
In Acipenser and Amia the adhesive organ intervenes between 
the hypophysis and the stomodeum. In Ammoccetes the 
upper lip occupies the same position as the adhesive organ of 
the Ganoids. This suggests the possible homology of the 
Ammoceetes upper lip with this adhesive organ. 
Von Kupffer believes the position of the hypophysis as 
found in these forms to be primitive, the hypophysis to be a 
