252 C. T. BRUES, 
Eggs in this stage, so far as my observations extend, are always 
confined to individuals that have not yet reached the adult state; 
i. e. have not undergone the final ecdysis and protruded the head, 
and seem usually to occur just before this instar. No doubt pre- 
cocious larvae may show this stage much earlier, as I have one 
specimen (a vernal larva) still a larva, that contains eggs advanced 
far beyond this stage. 
Aceumulation of the yolk. 
The eggs now begin to scatter more or less throughout the fat 
body, at first remaining confined to the previously mentioned two 
groups. But this separation into eggs of the right and left sides of 
the body gradually becomes less and less distinct as the eggs continue 
to spread through the fat body in all directions, and by the time 
each separate egg has become ripe they lie apparently without any 
orientation or arrangement. 
While this migration of the entire eggs within the body cavity 
of the female is taking place the eggs are being provided with yolk. 
When the complete number of nurse cells has been formed, the small 
nucleus of yolk begins to grow rapidly as a result of the degeneration 
of the cells in the egg. Those forming the polar cap are the first 
to begin to disintegrate (Fig. 3). The cap is in fact almost gone be- 
fore half of the nurse cells have been transformed into yolk. It still 
retains the original arrangement of its cells which have simply become 
flattened and resemble to some extent follicular cells. 
The cells of the polar cap are soon followed by the smaller nurse 
cells, in such a way that the yolk mass remains in the center of the 
egg, the cells about the periphery of the yolk degenerating completely 
before the more external layers take up the process (Fig. 4). Thus 
the ball of yolk keeps on enlarging through the stages shown in the 
figures until it occupies the entire egg and is surrounded by a thin 
membrane composed of a single layer of cells. 
This type of ripening is to some extent related to that occurring 
in some Lepidoptera and Diptera, where the nutritive and egg cham- 
bers are combined in one section of the ovarian tube, where they 
appear as a single swelling. Thus in an extremely early stage we 
find that the material for each egg has already been apportioned in 
the form of a mass of similar (to all appearances, at least) cells, 
which will give rise to nearly all the egg yolk as well as to the 
germinal vesicle. The comparatively very late differentiation of the 
