AGAMOGEJfESIS IN APHIDES. 385 



The viviparous forms diflfer essentially from the oviparous 

 forms in the structure of their reproductive organs. They pos- 

 sess neither spermatheCcTB nor coileterial glands, both of which, 

 as Von Siebold first demonstrated, are present in the females. 

 The young are developed within organs which resemble the 

 ovarioles of the true females in their disposition and may be 

 termed pseudovaries. The terminal or anterior chamber of 

 each pseudovarian tube is lined by an epithelium, which in- 

 closes a number of nucleated cells. One of the hindermost 

 of these cells enlarges and becomes detached from the rest as 

 a pseudovum. It then divides and gives rise to a cellular 

 mass, distinguishable into a peripheral layer of clear cells and 

 a central more granular substance, which becomes surrounded 

 by a structureless cuticula. It is this cellular mass which 

 gradually becomes fashioned into the body of a larval Ap)his. 

 A portion of the cells of which it is composed becomes con- 

 verted into a pseudovarium, and the development of new 

 pseudova commences before the young leaves the body of its 

 parent. It is obvious that this operation is comparable to a 

 kind of budding. If the pseudovum remained adherent to the 

 parental body, the analogy would be complete.* 



The agamogenetic multiplication of Cecidomr/ia-lsLryse is 

 an essentially similar process. Professor Nicolas Wagner, of 

 Kasan,' discovered that the larvoe of a Dipterous insect be- 

 longing to the genus Gecidomyia, or to a closely-allied form 

 {3flastor)^ multiply agamogenetically in the autumn, winter, 

 and spring. In summer, the final terms of the successive 

 broods of grubs thus produced are metamorphosed into 

 males and females, which copulate and lay eggs. From these, 

 larvae which exhibit the same phenomena, emerge. In this 

 case, the young are all developed from germs which are found 

 lying loose in the perivisceral cavitv of the parent, the body 

 of which they destroy and burst in order to become free. 



1872) should be consulted, not only on account of their richness in details, but 

 for the peculiar views which the author entertains respecting the nature of 

 the reproductive process in the Apliides. 



* Leydig (" Der Eierstock und die Samentasche der Tnsecten," "Nova 

 Acta," 1867) affirms that, in November, he has met with Aphides in which, in 

 the same animal, some of the ovarian tubes contain fullv-formed ova, and others 

 pseudova, undergoing: their ordinary method of development. Unfortunately 

 no information is afforded as to whether these aphides possessed a sperma- 

 tbeca, aud showed evidence of impregnation or not. The occurrence of aga- 

 mogenesis alongside of sexual propagation is in itself nothing unprecedented, 

 e. g., Pyrosoma. 



3 K. E. von Baer, " Bericht." (" Bulletin Acad. St.-P^tersbourg," 1863.) 



IT 



