No. 2. } BLATTA AND DORYPHORA. 303 
shape of half an elliptical disc, the short axis of which is to the 
long axis as 2 is to 3, with a thickness one-sixth of the short 
axis (Figs. 36 and 37). The egg is about 3 mm. long, I mm. 
broad and 4 mm. thick. Its volume is therefore almost a cubic 
millimeter. The cephalic end (Fig. 36 c), recognized by its 
evenly rounded contour, is immediately beneath the crista of 
the capsule. The opposite or caudal end (Fig. 36 s) is dis- 
tinguished by a slight sinus. The ventral face is traversed 
by a keel which runs from the cephalic to the caudal extremity 
and is most pronounced a short distance below the middle of 
the egg. The dorsal surface is flat and evenly curved antero- 
posteriorly. Cross-sections of the ovum are consequently pen- 
tagonal (Fig. 40). Thus the eggs can be easily oriented, and 
they have a great advantage over spherical or even oval ones, 
in that all the earliest developmental changes can be traced 
directly to their relationship with the parts of the future 
embryo. This is of the highest importance in the early stages. 
It will have been observed that a complete reflexion of the 
egg takes place during oviposition as the concave face of the 
curved ovarian egg becomes the convex back of the odthecal 
egg, and the convex micropylar face of the former becomes the 
straight, carinated, ventral face of the latter. 
Yolk. —I have not been able to observe a passage of fol- 
licular epithelial cells into the egg to form yolk by their dis- 
integration, as has been described by Will (51) in WVepfa and 
Notonecta, and by Ayers (1) in Gcanthus. There is only one 
layer of cells in the follicular epithelium of S/atta, and as this 
persists till after the chorion is completed, no migration of nu- 
clei into the yolk, or even disintegration of nuclei at the surface 
of the egg, is observable. All of the yolk in S/atta (excepting 
those portions derived from the germinal vesicle ?) is secreted by 
the protoplasm of the epithelial cells, not as yolk, but as sub- 
stances which are taken up by the growing ovule, and again 
secreted in the form of the bodies to be described presently. 
During this process of yolk-secretion, the epithelial cells re- 
main intact, their slow disintegration not taking place till after 
oviposition, when their compacted and yellowish remains have 
assumed the appearance so suggestive of the corpora /utea of the 
Mammalia. : 
The yolk of the eggs of B/atta has been studied by Patten 
