REPRODUCTION IN THE APHIDES. 341 



(893.) The Aphides, or plant-lice, furnish a remarkable instance of 

 fecundity. In these insects it has been satisfactorily ascertained, by 

 Bonnet, Lyonet, and Keaumur, that a single sexual intercourse is 

 sufficient to impregnate not only the female parent, but all her progeny 

 down to the ninth generation! The original insect still continues to 

 lay when the ninth family of her descendants is capable of reproduc- 

 tion ; and Reamur estimated that, even at the fifth generation, a single 

 Aphis might be the great-great-grandmother of 5,904,900,000 young 

 ones. 



(894.) The impregnated ova of the Aphis* are deposited at the close 

 of summer, in the axils of the leaves either of the plant infested by 

 the species, or of some neighbouring plant ; and the ova, retaining their 

 latent life through the winter, are hatched by the returning warmth of 

 spring, giving birth to a wingless hexapod larva. This larva, if cir- 

 cumstances, such as warmth and food, be favourable, will produce a brood 

 (or indeed a succession of broods) of eight larvce like itself, without any con- 

 nexion with the male. In fact, no winged females have, at this season, 

 appeared. If the virgin progeny be also kept from any access to the male, 

 each will again produce a brood of the same number of aphides ; and 

 careful experiments have shown that this procreation from a virgin 

 mother will continue to the seventh, the ninth, or the eleventh genera- 

 tion, before the spermatic virtue of the ancestral coitus be exhausted. 

 In the last larval brood, individual growth and development proceed 

 further than in the parent, and some individuals become metamorphosed 

 into winged males, others into oviparous females. By these the ova 

 are developed, impregnated, and oviposited, and thus provision is made 

 for disseminating the individuals, and for continuing the existence of 

 the species over the severe famine-months of winter t. 



(895.) This mode of reproduction is evidently referable to the 

 nursing system of Steenstrup ( 383) ; and inasmuch as, in the system 

 of nursing, the whole advancement of the welfare of the young is 

 effected only by a still and peaceful organic activity is only a func- 

 tion of the vegetable life of the individual, so also all those forms of 

 animals in whose development the nursing system obtains actually re- 

 mind us of the propagation and vital cycle of plants. For it is peculiar 

 to plants, and as it were their special characteristic, that the germ, the 

 primordial individual in the vegetation or seed, is competent to produce 



* Owen, Parthenogenesis, p. 24. 



f " The multiplication of these little creatures is infinite and almost incredible. 

 Providence has endued them with privileges promoting fecundity which no other 

 insects possess : at one time of the year they are oviparous, at another, viviparous ; 

 and, what is most remarkable and unparalleled, the sexual intercourse of one original 

 pair serves for all the generations which proceed from the female for a whole suc- 

 ceeding year. Reaumur has proved that in five generations one Aphis may be the 

 progenitor^of 5,904,900,000 descendants ; and it is supposed that in one year there 

 may be twenty generations." Kirby and Speuce, Introd. to Entom. vol. i. p. 175. 



