500 REIGHARD—MAST. [Vor. XIX. 
to the observation of von Kupffer (1893) in Acipenser, no 
connection was found between the hypophysis and the ento- 
blast, the cells of which may readily be distinguished from 
those of ectoblastic origin found in the hypophysis by the large 
round yolk granules they contain in contrast with the fine 
granules characteristic of ectoblast cells. Fig. 2, which is 
from a photograph, shows how distinct these two sorts of 
cells are and how sharply the ventral end of the hypophysis is 
separated from the entoblast. 
Fig. la represents a median longitudinal section of an em- 
bryo somewhat younger than that represented in Fig. 6 of 
the preceding article, from which Fig. 2 is taken. The section 
is slightly oblique. It shows the hypophysis more broadly 
connected with the neuropore at its dorsal end than in Fig. 2, 
and lying against the posterior face of the button. Otherwise 
the condition of the hypophysis is not greatly different from 
that shown in Fig. 2. 
In the fourth stage of the preceding article, the hypophysis 
(Fig. 3, hy.) has lost its connection with the ectoblast entirely 
and lies in a horizontal position in the somewhat enlarged 
space between the forebrain and the adhesive organ close to 
the dorsal wall of the alimentary canal with its posterior end 
projecting into the angle between the forebrain and the dorsal 
wall of the alimentary canal. The hypophysis considered as 
a solid has become somewhat tongue-shaped, and is now com- 
posed of a mass of more or less cubical cells. No definite 
arrangement of these cells could be determined. It contains 
three small inter-cellular cavities, none of which were found 
in younger stages. These cavities, some little distance apart, 
are situated on a median longitudinal line a little nearer the 
posterior than the anterior end of the mass of cells. 
A stage between Figs. 2 and 3 is represented in: Fig. 2a. 
The hypophysis is here more recently separated from the 
neuropore than in the stage of Fig. 3. The embryo from 
which this section was taken is externally scarcely distinguish- 
able from that shown in Fig. 6 of the preceding article, except 
by the single character that its tail is free from the yolk for 
a distance equal to thirty degrees of the yolk’s circumference. 
