A contribution to our knowledge of the Stylopidae. 253 
single large egg cell proper with its nucleus causes the entire pheno- 
menon of oogenesis to assume a very different aspect from that pre- 
sented by insects where the egg cell proper grows and differentiates 
itself from its attendant nurse cells at a much earlier stage. It can 
be readily seen that such a delay in this period of growth could 
bring about the conditions which we see in Xenos. 
In some eggs which are just beginning to form the yolk, I have 
observed a difference in size among the nurse cells; i. e. one or pos- 
sibly two of considerably larger size than their fellows, but of ex- 
actly similar appearance. I cannot believe that one of these larger 
cells may represent the germ cell, for it seems to degenerate into 
yolk like the others. 
One should expect to find exactly the opposite of what actually 
takes place with regard to the time of differentiation of the definitive 
egg cell in Xenos. The extremely precocious development of the re- 
productive organs and the early stage at which the eggs begin to 
form in the ovaries ought to lead to a very early appearance of the 
germinal vesicle in the egg. Evidently the peculiar method of egg 
nourishment must influence it in an opposite direction. 
On the whole this method of egg ripening is quite peculiar and 
seems worthy of being placed in a separate category among the 
various types presented by insect eggs. 
Miss CLAYPOLE (98) has described at length the oogenesis of 
Anurida, one of the Thysanura, which presents a condition somewhat 
resembling that occurring in Xenos, and from which the latter could 
be perhaps derived. In Anurida each egg is rather definitely as- 
sociated with a number of nurse cells. The eggs with their attendant 
nurse cells are not distinctly separated from one another, however, and 
lie loosely in swellings of the ovarian tube. The early formation of 
separate cavities for the developing eggs in Xenos cause the eggs to 
appear as distinct units at such an early age. Here also, a much 
larger number of more specialized nurse cells are present. But I do 
not_ believe that much significance can be attached to any of these 
resemblances as the Stylopidae are evidently far removed from both 
the Thysanura on the one hand and the Lepidoptera and Diptera 
on the other. 
Form and Structure of the Ripe Egg. 
The eggs of Xenos are broadly oval, and slightly attenuated at 
the pole at which the embryo will first make its appearance. In cross 
Le 
