A contribution to our knowledge of the Stylopidae. 251 
time, until the larva has undergone another ecdysis and begun to 
assume the form of a full-grown female larva. A mass of nurse cells 
now begins to form in the cavity of each primitive egg, causing a 
great increase in size. Most probably more than one egg is formed 
from each of the primitive eggs of the previous stage, perhaps two or 
three. This point could not be exactly determined, but a consideration 
of these two stages with regard to the total number of eggs in various 
animals proves that an increase in number surely takes place. The 
great number of nurse cells which are formed are only partly enclosed 
in the cavity of the primitive egg, for their growth has caused the 
egg to burst. A part of this egg remains attached to each mass of 
nurse cells and forms a sort of cup in which they rest (Fig. 2). 
The eggs have now become distinctly separated, although they 
are still confined to two distinct regions, one on each side of the in- 
testine. Each of these groups lies in a cavity of the fat-body, the 
eggs still being too close together to allow the strands of fat cells to 
penetrate between them. Apart from the large polar cap of cells, 
each egg is enclosed in a delicate follicular membrane composed of 
extremely flattened cells and apparently almost structureless in many 
places. It is probably derived from the follicular membrane of the 
previous stage. Most of these large cells are of nearly equal volume 
and arranged with their apices together, the cells forming the layer 
directly above the nurse cells being necessarily shorter on their long 
axis than the others. The size of this cap is somewhat variable in 
different eggs and is often considerably larger than the one shown in 
the figure, as its edges sometimes almost reach the equator of the 
egg. The future oval shape of the egg has already become apparent, 
the cap and nurse cells always together assuming this oval form. 
Thus the external form and size remain very nearly constant, while 
the entire yolk mass is being stored up. This is of course the result 
of the early apportionment of a sufficient number of nurse cells to 
each egg to supply all the nourishment necessary for its complete 
growth. These large cells evidently take the initiative in the secretion 
of the yolk which has hitherto been entirely absent. Yolk can now 
be seen at the apices where the cells meet at a common point. The 
amount of yolk there deposited is very small but evidently forms the 
nucleus for subsequent additions to the mass of yolk which is de- 
stined to arise from the degeneration of the cells now in the egg. 
Apart from the delicate follicular wall of extremely flattened and 
attenuated cells, the egg is at present entirely without envelopes. 
Zool. Jahrb. XVIII. Abth, f. Morph. 117 
