108 On the Reproduction and Embryogeny of the Aphides. 



developed testis; but in the female it is otherwise, and we shall 

 see, in speaking of the development of the egg, that its presence 

 in this sex has a much more important signification. 



The conditions which influence the determination of the sexes 

 in the Aphides are probably of the same kind as those which 

 act in a more general manner to bring on a change in their 

 mode of propagation ; that is to say, they are probably depen- 

 dent upon the phenomena of nutrition in these insects. The 

 following observations support this opinion. 



At the period when the production of the dioecious genera- 

 tions commences we find that at first females are almost exclu- 

 sively generated, the males being still comparatively rare. But 

 the latter soon become more and more numerous, and at last 

 are even produced in greater abundance than the female indivi- 

 duals. A single hermaphrodite mother may, moreover, contain 

 at the same time embryos of both sexes, succeeding each other 

 without apparent order in the interior of her ovarian sheaths. 

 It is curious to observe the diff^erence of coloration of the male 

 and female embryos of the same species. The latter alone pre- 

 sent a colour which resembles that of their mother : thus, for 

 example, in a species of which the viviparous individuals are 

 brown, the oviparous females are also brown, whilst the males 

 are constantly green*, and vice versa. This difference of colour 

 is due to the oleaginous globules which fill the cells of the fatty 

 body, and is, no doubt, connected with a different chemical 

 composition of the nutritive fluids in the embryos of the two 

 sexes. 



After this brief exposition of the embryogenic phenomena 

 connected with the determination of the sexes in the Aphides, 

 it remains for me, in order to traverse the whole reproductive 

 cycle of these animals, to describe in few words what I have 

 been able to observe of the development of the ovum destined to 

 reproduce the viviparous generations with which we commenced 

 this investigation. Notwithstanding the considerable diffeiences 

 as to its elementary constitution and the conditions of its deve- 

 lopment presented by the voluminous ovum of the oviparous 

 Aphides when compared with the little ovule of the viviparous 

 individuals, there is nevertheless a striking analogy in the phe- 

 nomena of which both are the seat. Although the formation of 

 the embryo does not commence in the former until after it has 

 been fecundated by the male and brought into the world, it 

 nevertheless, whilst still enclosed in the ovary, exhibits pheno- 

 mena which indicate that genetic operations have already begun 

 in its interior. Thus we observe, at the posterior pole of this 



* At least in the embryonic and larval states ; the adult male is almost 

 always blackish. 



