No. 2.] THE AYPOPHY SIS OF AME. 499 
tened. The original anterior end of the hypophysis is now 
directed postero-ventrally and projects into the slightly acute 
angle formed by the floor of the forebrain and the dorsal 
wall of the alimentary canal. The posterior surface (ventral 
surface of the preceding stage) comes in contact near its dorsal 
end with the wall of the forebrain in the region of the lobus 
olfactorius impar and near its ventral end with the wall of the 
forebrain in the infundibular region (Fig. 2, in.). The cen- 
tral portion of the posterior surface is separated from the fore- 
brain by a mass of mesenchyme cells which in the preceding 
stage was situated between the anterior end of the forebrain, 
the dorsal wall of the alimentary canal, and the ventral surface 
of the hypophysis. The anterior surface of the hypophysis, 
which in the preceding stage was the dorsal surface and which 
was then in contact with the outer layer of ectoblast, is now 
it: contact with the adhesive organ and button, which, develop- 
ing from the crescent of the preceding stage, have grown up 
and separated the hypophysis from the ectoblast and forced 
it against the anterior wall of the forebrain. The cells com- 
posing the hypophysis are more or less columnar in form, 
arranged so that their longitudinal axes are approximately 
parallel with the longitudinal axis of the hypophysis, especially 
at its dorsal end, as if the entire organ had been forcibly 
elongated. 
Mechanically, the change in the position and form of the 
hypophysis between stages I and 2, may be referred to the 
rapid enlargement of the cavity of the forebrain and to the 
development of the adhesive organ. The enlargement of the 
cavity of the forebrain causes the ectoblast in front of the 
neuropore, which in the preceding stage was nearly parallel 
with the dorsal wall of the alimentary canal to assume a posi- 
tion nearly at right angles to it. The upgrowth of the adhe- 
sive organ at the same time separates the hypophysis, ante- 
riorly and laterally, from the ectoblast, and as already stated 
forces it against the anterior wall of the forebrain. 
Sections of several embryos both older and younger than 
those of the stage just described were studied, but, contrary 
