426 
PROF. B. T. LOWNE ON THE STRUCTURE AND 
The whole ovary has also altered its position ; the surface from 
which the oviduct originates is now turned towards the ventral 
aspect of the insect, so that the long axes of the egg-follicles are 
transverse to the axis of the body. I shall still, however, call the 
end of the egg-follicle which is nearest to the oviduct, posterior, 
to facilitate comparison and avoid confusion. 
The ovarian follicles are now more fully developed, and loosely 
invest the posterior part of the egg-strings. The anterior part, 
the terminal chamber, is closely covered by the anterior part of 
the follicle, which is so thin that it can scarcely be traced as a 
distinct layer. The posterior part of the egg-follicle exhibits a 
distinct epithelial layer, which is continuous with the epithelium 
of the calicine duct, and the follicles open freely into these ducts. 
The three parts of the egg-string are very distinct, within a very 
fine cuticular tunica propria. The stalk is filled by a single layer 
of epithelium ; there is no lumen and no double epithelial layer ; 
but where the stalk enlarges near the egg-chamber there is more 
than a single layer of cells, but these are irregularly arranged. 
The egg-chamber, when fully formed, contains a group of 
yelk-cells flattened by mutual pressure and surrounded by an 
epithelial capsule (ec), which is continuous with the cells of 
the stalk. 
In some of the tubes a second egg-chamber is seen in process 
of formation (PI. XXVIII. fig. 7), with a cup-like epithelial in- 
vestment. In others the first egg-chamber is in the same con- 
dition; the cells destined to form the egg are still round and 
scarcely differentiated from those of the terminal chamber. It 
appears to me that the epithelial investment of the ovum grows up 
from the stalk, aud that all the cells of the terminal chamber 
develop into yelk-cells. 
The gradual transition from the small round cells of the 
terminal chamber to yelk-cells is very marked, so also is the 
upper edge of the epithelial cup (fig. 7, y), which ends abruptly in 
a thin edge, whilst the continuity of the epithelium of the stalk 
and of the egg is equally distinct. 
The large yelk-cells stain very deeply with alkaline carmine, 
and the colour is not washed out by 5 per cent, solution of acetic 
acid. They average 12 y in diameter, and all the cells in an egg 
are precisely similar, and have nuclei which are rich in 
chromatin granules. There is no cell with a clear nucleus, and 
nothing which I can recognize as a germinal vesicle. 
