530 THE AMERICAN NATURALIST. [Vor. XXXVI. 
deeply pigmented cells, and they are apparently exactly like 
the small cells forming the upper surface of the egg, except 
that they do not contain quite as much pigment. The yolk 
cells which form the floor of the archenteron are three or 
four times larger than the cells of the dorsal wall, and they 
are more rounded and 
contain little if any pig- 
ment. The distinction 
between these cells is 
made more evident by 
the fact that with the 
7^5 combination stain used 
EJ ) all the yolk cells appear 
EENT decidedly blue, while the 
SILT Te $ lls of the dorsal wall of 
3 XR SI) D cells of the dorsal v 
> Se [o] 97) 


eS A VIR ^y: 
m 
zo E LETT F 

S.C. 

the archenteron and, in 
fact, all the cells of the 
upper hemisphere, take 
a distinctly reddish tint. 
The cells at the anterior 
end of the archenteron 
are still wedge-shaped at 
this stage. They are 
intermediate in size be- 
tween the cells forming 
the dorsal wall and those 
forming the ventral wall 
of the archenteron, and 
they stain like the yolk 
gn gus as = a — MA the median plane of cells. a 
aT at eed Fe seme In opposition to most 
eee ee re; M,cls investigators, Moquin- 
Tandon (15), Houssay, 
Robinson and Assheton (20), and Marshall (14) maintain that 
the archenteron of the amphibian embryo is not formed 
by a process of invagination, but by a splitting between 
yolk cells which thus form the dorsal as well as the ventral 
wall of the archenteron. In a later paper, Assheton (1) 


