532 THE AMERICAN NATURALIST. [Vor. XXXVI. 
The presence of pigment in the inner ends of the cells 
forming the dorsal wall of the archenteron has been explained 
` by Robinson and Assheton as follows: “The pigmented area 
is produced and extended by the deposit of pigment in the 
adjacent margins of a double row of yolk cells which eventu- 
ally will form the boundary wall of the archenteron, and it 
BRE also radiates from this 
X^ area along the adja- 
DE 
. E 
DA 
Sy 
ane 
Fic. 11. — Part of 
pore at the stage of 
as in previous figure 

di agittal section through the blast 
Fig. 2. EC., ectoderm. Other lettering 
s. 

? cent margins of the 
cells of each row. A 
slit-like space appears 
in the middle of the 
posterior portion of 
the pigmented area. 
This space first limits 
the dorsal lip of the 
blastopore, and then 
extends forward and 
ventrally, following 
the deposit of pig- 
ment, and separating 
the two rows of mar- 
ginaly pigmented 
cells from each 
other.” During the 
early stages of gastru- 
lation there is always 
found at the anterior 
end of the archen- 
teron a marked accu- 
mulation of pigment 
that is extended 
around to include a 
few of the yolk cells 
in this region (Figs. 
IO—12). I have never found more than a few scattered pigment 
granules in the lower yolk cells except in this particular part 
of the egg, and, if the archenteron is formed by a splitting 
