No. 2.] BLATTA AND DORYPHORA. 329 
narrow oval pit which is visible till the mouth begins to in- 
vaginate (Fig. 73 a). 
While the amnion and serosa are closing over the oral portion 
of the embryo the yolk begins to segment. The first traces of 
segmentation are visible on the dorsal surface between the end 
of the tail and the procephalic lobes. There the surface of the 
yolk assumes a scalloped appearance, and radially directed lines 
soon mark the divisions between the yolk balls. The segmen- 
tation progresses thence in a ventral direction, both from either 
side of the dorsum and directly inwards, so that finally the whole 
yolk is reduced to rounded masses, each of which contains from 
one to three vitellophags. Each yolk segment is properly a cell 
with its protoplasm radiating in all directions as a delicate 
reticulum which holds in its meshes the unequal-sized yolk 
spheres. By the time the amnion and serosa have completely 
formed, all the yolk has been converted into distinct subspher- 
ical segments, except the portions immediately under the anal 
and oral ends of the gastrula. Here the segmentation remains 
for a short time indistinct till the entoderm is established at 
these points. 
In the embryo with completely closed envelopes (Fig. 73, 
Pl. V.) the procephalic lobes (fc/) have grown in size, and 
when attached to the egg clasp its upper pole. The three pairs 
of thoracic limbs are distinctly formed, while of the cephalic 
appendages only the 2d maxillz (mx 2) are beginning to appear. 
The base of the attenuated ribbon-shaped abdomen shows traces 
of commencing segmentation. Posteriorly it suddenly widens 
out into a flat, transversely oval body, which I shall call the caudal 
plate. The gastrular invagination is closed except at its anal 
end (x 73), and the mouth will soon form at the shallow oval 
depression a, which marks the anterior end of the groove. 
Fig. 82 represents a longitudinal section through an embryo 
a very little older than the one just described (Fig. 73). 
The serosa (sv) now covers the entire egg, and is separated 
from the embryo proper and the amnion (am). Both mem- 
branes present the same appearance in section, being nodulated 
with nuclei. The anterior end of the embryo lies on the anterior 
end of the yolk in such a position that its mouth (s/) is almost 
exactly at the pole; the tail ends somewhat anterior to the mid. 
dle of the dorsal surface (vy), The ectoderm, which at its cephalic 
