Nor2))) 227CRODEUTOPUS (GRYLLOTALPA COSTA. 319 
the ventral surface (Fig. 38, add.) in the region of the first 
abdominal appendage. Figs. 40-42 are three views of the 
same egg. At this stage the appendages no longer extend 
over the dorsal surface (cf. Figs. 36 and 40), although they still 
cover the lower pole of the egg (Fig. 41). The anlagen of the 
seven abdominal appendages are pushed inwards, and finally all 
lie in the abdominal fold (Fig. 43), whereas the space between 
the dorsal organ and the last appendage extends over the whole 
lower hemisphere of the egg. 
The mode of formation of the abdominal fold in Microdeuto- 
pus differs widely from that in Orchestia, judging from the 
comparison of Figs. 36-43 for Microdeutopus with those of 
Orchestia, as figured by Della Valle (93). 
Entoderm. 
The entoderm in Microdeutopus arises as a true invagination 
at the hind end of the embryo. During the second day, when 
the ventral plate has completely overgrown the egg, the cells 
immediately behind the dorsal organ invaginate. These cells 
migrate into the interior of the egg, and there arrange them- 
selves to form the liver tubes and the greater part of the digest- 
ive tract. The entodermal invagination is shown in optical 
section in Fig. 37 (ez. zv.), and Fig. 53 represents a trans- 
verse section passing through the center of the entodermal sac, 
while in Fig. 54, which represents a small portion of a sagittal 
section, the relative position of the entodermal invagination 
and the dorsal organ are shown. In this egg the cells of the 
dorsal organ have the characteristic bottle shape which is 
peculiar to them, but the ends of the cells still contain granu- 
lar protoplasm; later they are filled with some clear, unstain- 
able substance. . 
A section of an egg a little older (Fig. 55) shows the cells 
of the entodermal sac migrating into the interior as an irregu- 
lar mass. These cells distribute themselves throughout the 
yolk area, the greater number, however, remaining in the 
region at which they entered. These are the first cells which 
appear in the center of the egg, excepting the two blastomeres 
