572 AGAMIC REPRODUCTION OF APHIDES, &C. 



very short time ; arid one viviparous brood succeeds another, 

 so long as adequate warmth and food are supplied. Ten or 

 twelve are thus commonly put-forth in a single season ; and 

 as each brood may consist of a hundred individuals, it may 

 be easily calculated that no fewer than ten thousand million 

 million of Aphides may thus be produced in one summer from 

 a single individual. With the advance of autumn, however, 

 the last brood of larval Aphides, instead of continuing to 

 propagate after this fashion, is developed into the perfect 

 sexual form ; distinct males and females present themselves 

 the true generative process is performed ; and, as its result, 

 eggs are deposited, that are capable of resisting the cold of 

 winter, which would be fatal to the viviparous larvae. From 

 these eggs, larval Aphides are hatched in the spring, which 

 repeat the same curious series of phenomena. Recent in- 

 quiries have shown that this method of propagation is by no 

 means confined to the Aphides, but is common to many other 

 Insects. Thus, it appears that the various species of Cynips 

 or gall-fly (ZooL. 755) are for the most part known only 

 under the female type, and that they can propagate without 

 any male ; the eggs which they deposit producing larvas, which 

 are developed into the likeness of their parents without re- 

 ceiving any fertilization. It may be surmised that, as among 

 Aphides, males make their appearance under certain condi- 

 tions, and that a proper generative act occasionally intervenes 

 between the successive productions of non-sexual broods. 

 Comparing these phenomena with those of the gemmation of 

 Salpa3 ( 728), and with other cases of like nature, it might 

 be supposed that the non-sexual or agamic 1 production of 

 Aphides, Cynipidce, &c. is only another case of the same kind. 

 But there is this peculiarity about it, that the young are 

 produced, not from buds, but from bodies having all the 

 characters of ordinary eggs. And it would seem, from the 

 facts next to be mentioned, that in certain cases the same 

 ovum may develope itself either with or without fertilization j 

 its product in the two cases, however, being different. 



747. Among Bees, Wasps, Ants, and other social Insects, 



the generative process is performed in a very peculiar manner. 



By far the larger proportion of their communities are neuters, 



that is, are incapable of reproduction ; the continuance of the 



1 From o, not ; and 7o ( uoy, marriage. 



