506 Royal Society. 



the egg-formation from that which occurs in any other Hymenopterous 

 insect. 



The mature egg of Cynips is indeed of a very remarkable shape, 

 as it consists of a long tube with a small swelling at one end, and a 

 larger one at the other, in which the yolk is situated. The larger 

 end occupies the usual place of the egg, but as the tube elongates, 

 the smaller end pushes its way up the egg- tube, which elongates 

 considerably ; and, finally, all the large ends are at the lower end, and 

 the small ones at the upper end, of the egg- tube, which gives the 

 ovary a curious appearance. Even after the egg is fully formed, a 

 slight pressure will bring the germinal vesicle into view. 



Many of the Lepidoptera have presented us with cases of Parthe- 

 nogenesis, and in these instances there is no reason to suppose that 

 the formation of the eggs differs from the usual type. The same 

 holds good in Solenobia lichenella, in which agamic eggs are the rule, 

 instead of the exception. 



In the Hive-bee also, the early development of the ova and of the 

 pseudova must apparently be identical, since it would appear that in 

 an impregnated female, the ovarian product has already left the 

 ovary before it is decided whether it is to become an ovum or a 

 pseudovum, and whether it is to give birth to a male or to a female. 



It is, therefore, I think, proved that we must not look in the ovarian 

 egg for differences necessarily depending on sexual influence, but 

 that we shall find them, if anywhere, in the subsequent stages of egg- 

 development. 



Prof. Huxley and Leuckart have recently shown, that whereas the 

 vitelligenous cells are well developed in the oviparous Aphides, they 

 are much less apparent in the agamic or viviparous forms ; so much 

 so indeed as to make these naturalists doubt whether they take any 

 part in the secretion of the yolk. While waiting for the publication 

 of Prof. Huxley's observations, I have paid but little attention to the 

 Aphides ; but it struck me as a curious coincidence, that, in Coccus 

 also, while the viteUigenous cells are very distinct in the oviparous 

 C. PersiccBy they are much less apparent in the almost viviparous 

 C. hesperidum. It would of course be highly unphilosophical to 

 draw any conclusion from four instances ; but it will be curious if the 

 same connection between oviparity, and the presence of well-de- 

 veloped vitelligenous cells on the one hand, and viviparity, with less 

 developed vitelligenous cells on the other, is found to prevail in other 

 species. 



It has been generally stated that all species of Aphides are, in 

 spring and summer, self-fertile and viviparous, and become in autumn 

 oviparous, while the eggs require impregnation. I cannot, however, 

 help thinking it probable, that in cold and in mountainous regions, 

 where at any period of the year frosts may occur, we shall find species 

 which are always oviparous (as indeed is said to be the case with 

 Aphis Abietis) ; while in tropical regions, where frosts are unknown 

 and leaves are less often deciduous, other species may occur which 

 are naturally viviparous all through the year, and whether or not 

 they have undergone impregnation. . 



