A contribution to our knowledge of the Stylopidae. 957 
seen in Fig. 10 where the rudiment of the germ band is really a sort 
of morula. The embryo has also increased in size and now occupies 
almost one-third of the egg. A differentiation has occurred in the 
nutritive elements also, through the formation of a continuous and 
homogeneous envelope of transformed yolk which encloses both the 
embryo and the interior yolk globules, lying directly inside the chorion. 
This new yolk acts differently toward stains than the primitive kind, 
not retaining the iron haematoxylin so tenaciously but staining much 
more deeply with orange G. In Fig. 14 it can be seen stained bright 
yellow with a few large black spots here and there. The primitive 
yolk under the same conditions is of a paler yellow and with much 
smaller and more numerous black spaces. DELAFIELD’s haematoxylin 
stains the peripheral yolk slightly but fails to color the interior yolk 
at all, indicating perhaps that it may approach more nearly to proto- 
plasm in composition. This may be analogous to the .secondary 
yolk formation which has been observed by WıLL in Aphis. It should 
be noticed that the eggs are under similar conditions in the two 
cases: i. e. developing in the fat body of the mother. 
This morula-like mass of cells soon gives rise to a_ typical 
gastrula through the formation of a small internal cavity. The sur- 
face of the gastrula which rests upon the surface of the yolk, is flat 
and composed of an almost cuboidal epithelium while the upper portion 
is dome-shaped and formed of columnar cells (Fig. 11). The embryo 
now contains the largest cells which are formed during the entire 
embryonic development and occupies nearly one half of the interior 
space of the egg. The number of cells in the embryo has increased 
during the changes between the blastoderm and gastrula and is now 
about 144. Up to the present time no vitellophags have been visible 
in the yolk but they now begin to appear. They are about six or 
seven in number and seem to persist individually as long as any yolk 
remains. I have not been able to determine from which cells the 
vitellophags arise. 
= The hollow sphere of cells ceases to increase in size, but numerous 
divisions occur, increasing the number of cells considerably and cor- 
respondingly decreasing their size. No deviation from a simple hollow 
sac of one layer is apparent, for all the cells remain as long as be- 
fore, their cross section being the only dimension lessened by division. 
The shape of the embryo changes at the same time and becomes con- 
siderably flattened and regularly oval in form (Fig. 12). 
