426 PEOF. B. T. LOWNE ON THE STRTTCTtTRE ANB 



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 tliese 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 difi'erentiated from those of the terminal chamber. It 

 appears to me that the epithelial investment of the ovum grows up 

 from the stalk, and 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 fx 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. 



