10 INTRODUCTION. 



body " and K germ-stock " for these reproductive organs of the 

 viviparous Aphides, in order to distinguish them, on account of 

 their different physiological import, with regard to the alterna- 

 tion of generations, from the eggs and ovaries of the oviparous 

 female Aphides. 



Owen* has regarded the asexual viviparous Aphides as virgin 

 females capable of reproduction ; but these viviparous Aphides 

 indicated by Owen as virgin parents are certainly something 

 very different from the oviparous Aphides in their virgin state 

 before copulation. For the same reason also I cannot approve 

 of Owen's expression Parthenogenesis, as applied by him to the 

 alternation of generations, as under the term Parthenogenesis I 

 do not understand reproduction by asexual nurse-like or larval 

 creatures, but a reproduction by actual females, that is to say, 

 by individuals furnished with perfectly developed, virgin female 

 organs, which produce eggs capable of development without pre- 

 vious copulation and in an unfecundated condition. 



* On Parthenogenesis, or the successive production of procreating indivi- 

 duals from a single ovum. London, 1849, pp. 30, 60, & /6. 



[By reference to this work, it will be seen that, in the description of the 

 parthenogenesis of the Aphides, the viviparous individuals are called * larvae,' 

 and the basis or blastema of the virgin-progeny ( germ-masses' : both are ex- 

 pressly distinguished from the true ova and oviparous females. 



" The facts are briefly these : — 



" 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 : a wine/less hexajwd 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 winged 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 will continue to the seventh, 

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

 ancestral coitus has been exhausted. When it is so exhausted, a greater 

 proportion of the nuclear germ-masses retained by the last procreant larva? is 

 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. By these the ova are developed, im- 

 pregnated, and oviposited."— Owen's ' Parthenogenesis,' p. 23.] 



