INTRODUCTION. 



rative organs, and which had previously been looked upon as 

 virgin female Aphides, as Nurses (Ammen), and consequently as 

 those members of an animal-species subjected to an alternation 

 of generations, which are capable of producing young in the 

 asexual (or larval) state. Those Aphides which bring forth living 

 young without a preliminary copulation, are in reality quite dif- 

 ferent in their organization from the true female Aphides, which 

 lay eggs capable of development after the act of copulation. In 

 the viviparous Aphides those organs especially from which the 

 living young are produced, have quite a different form and organi- 

 zation from the sexual organs of the oviparous female Aphides, 

 so that, in opposition to the ovaries (Eierstocke}, the products of 

 which (eggs) only become capable of development by the action 

 of the male semen, we may with perfect justice indicate these 

 organs as germ-stocks (Keimstocke), which are capable of pro- 

 ducing young of themselves, without the influence of male fer- 

 tilizing organs. These nurse-like, viviparous Aphides therefore, 

 which instead of ovaries bear germ-stocks in their interior, are 

 also destitute of the seminal receptacle, which occurs universally 

 in the females of Insects and plays an important part in the act 

 of fecundating the eggs*. Before the alternation of generations 

 had yet been introduced into science by Steenstrup, I had al- 

 ready called attention to the different conditions of organization 

 in the oviparous and viviparous Aphides, and especially to the 

 absence of the seminal receptacle in the latter f. Subsequently 

 the development of the Aphides without fecundation has been 

 completely explained by V. Cams}, as a process of the alterna- 

 tion of generations. The representation which Carus has given 

 of the development of germinal bodies in the germ-stocks of the 

 viviparous Aphides, has certainly met with a refutation from 

 Leydig, against which I have nothing to object; nevertheless, 

 although, according to Leydig, the young are developed from 

 the germ-bodies of the viviparous Aphides exactly as from eggs, 

 by cell- formation, I would retain the denominations "germ- 



* See my Observations on the Spermatozoa in fertilized female Insects. 

 Mailer's Archiv, 1837, p. 392. 



t See Froriep's Neue Notizen, Bd. xii. 1839, p. 308. 



J Zur ndheren Kenntniss des Generationswechsels, 1849, p. 20. 



Bemerkungen uber die Entwickelung der Blattlduse in Siebold und Kolli- 

 ker's Zeitschrift fur wissenschaftliche Zoologie, 1850, p. 62. 



