GENERATION OF INSECTS. 409 



insight into the circumstances which rendered the successive genera- 

 tions from virgin Aphides possible and conceivable ; and I have the 

 greater confidence in the truth of that insight from having found it 

 equally explanatory of the analogous phenomena of " Lucina sine 

 concubitu " in other animals. 



It is now more than a century since Bonnet, in his " Traite d'ln- 

 sectologie," 8vo., 1745, first attracted the attention of physiologists 

 and naturalists to this mode of generation in the Aphides, or plant- 

 lice. And because it was the first of a large class of phenomena, till 

 then utterly unknown and unsuspected, it was received with consider- 

 able doubt, or met by total incredulity. 



The facts are briefly these : — 



The impregnated ova of the Aphis are deposited, at the close of 

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

 species, and the ova, retaining their latent life through the winter, 

 are hatched by the returning warmth of spring : a wingless hexapod 

 larva is the result of the development. This larva, if circumstances, 

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

 indeed, a succession of broods, of eight larvce like itself, without any 

 connection with the male. In fact, no Avinged males, at this season, 

 have 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 carefully prosecuted experiments have shown that this 

 procreation from a virgin mother may continue to the seventh, the 

 ninth, or even the eleventh generation before the spermatic virtue of 

 the ancestral coitus has been exhausted. 



When it is so exhausted, a greater proportion of cells in the 

 germ-masses developed from the remnant retained by the last pro- 

 creant larvae are used up : individual growth and development proceed 

 further than in the parent ; some members of the last larval brood 

 are metamorphosed into winged males, others into oviparous females ; 

 the ova are 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. 



These phenomena, first observed, as I have said, by Bonnet, in the 

 genus Aphis, were the first to which the thoughts of physiologists 

 were bent to explain. But, being viewed in the light of an anoma- 

 lous exception, and at a period when the phenomena of embryonic 

 development were not known, the earliest steps more especially, 

 success could not be expected. 



Reamur eluded the difficulty of the fact which Bonnet had dis- 

 covered, by affirming the Aphides to be androgynous. The vagina 



