EMBRYOLOGY OF COCCIDS 85 



The chorion is a very thin membranous structure which en- 

 closes the substances above mentioned. It is formed shortly 

 before the passage of the egg from the egg chamber into the 

 uterus, and is secreted by the follicular epithelial cells. 



The protoplasm or cytoplasm fills, so to speak, most of the 

 space between the other inclusions of the egg, with the exception 

 of the space occupied by the nucleus or the germinal vesicle. 

 As already stated, this ground substance of the egg is elaborated 

 by the nurse cells and is literally poured on the egg. At first 

 the protoplasm is a homogeneous mass uniformly surrounding 

 the central clear region, the nucleus. Later, however, it becomes 

 mesh-like, owing perhaps to the more rapid expansion of the egg 

 than the flow of the nutritive or protoplasmic substance from 

 above, to the intrusion and consequent suspension of other sub- 

 stances, and also to the physiological change due to the metabolic 

 activity of the germinal vesicle. 



What seems to me a sort of yolk substance is found in the egg 

 of the mealy bug of the giant ragweed. This substance may be 

 spherical, but it is more often irregular in shape. It first appears 

 at about the time when the germinal vesicle reaches the periph- 

 ery. The exact origin of this substance remains to be studied 

 further. The fact that similar granules are abundant in the 

 body cavity surrounding the ovarioles, and also in spaces between 

 the chorion and the epithelial cells, strongly suggests that these 

 particles may actually migrate from the body of the mother 

 through the epithelial layer into the egg. The presence of 

 similar substances in the body cavity of the mother is another 

 evidence in favor of the view just stated. Several investigators 

 of other insect eggs state that they have observed the migration 

 of chromatin matter from the germinal vesicle of the egg. No 

 indication of such migration was observed in the case of the 

 scale insects studied. 



In the ovarian eggs of these species of coccids, the nucleus or 

 the germinal vesicle was always found. 



The pigment-oil or coloring matter appears in the mature, but 

 not in the ovarian egg. I have had occasion to observe this 

 fluid-like matter flowing into the egg at the posterior or pointed 



