28 



cell already exists in her with sufficient spermatic and 

 plastic force for its development : no semen, therefore, 

 needed to be retained, and there is no spermatheca : the 

 embryonic development is completed in utero, and no se- 

 cretion for the protective covering of ova was needed. The 

 structures therefore which Reaumur, under a misconception 

 of their nature, cited in order to solve the problem of 

 the alleged virgin procreation, are present only in that 

 perfect form of Aphis where no such phaenomena are mani- 

 fested*. 



Leon Dufour, whose extent of research and comparison 

 of the generative organs of insects led him to a true appre- 

 ciation of the nature and function of the appendages to 

 the female organs of the oviparous Aphides, referred the 

 phaenomena of the generation of the larviparous Aphides to 

 * spontaneous or equivocal generation/ Now if we con- 

 sider what we actually learn from these words, that the 

 larvae produced by the virgin Aphides are produced by 

 ( spontaneous ' or equivocal generation, it will seem to be 

 little more than another mode of stating the fact. The 

 condition or mode of the fact, i.e. the phaenomena rendering 

 it possible, are not explained by them : M. Leon Dufour, 

 however, meant to record his belief in a hypothetical mode 

 of generation, in which, as he expresses it, f the act of im- 

 pregnation was in no degree concerned/ Having detected 

 the male Aphis and well scrutinized the structure of its 

 organs, having witnessed the coitus with the winged female, 

 and carefully excluded the male in repeating the observa- 

 tions and experiments of Bonnet, M. Dufour satisfied 

 himself, and affirmed, that impregnation had no share what- 

 ever in the phaenomena of the development of the larval 

 aphis in the body of another virgin larval aphis. 



With regard to the hypothesis of spontaneous generation, 

 the reasons which have led me to concur with most physio- 

 logists of the present day in rejecting it were fully given in 

 * Siebold, in Froriep's Notizcn, Bd. xii. p. 308. 



