572 AGAMIC REPRODUCTION OF APHIDES, &c. 
very short time ; and 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 larve. 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 (Zoou. § 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 larvee, 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 
Salpz (§ 728), and with other cases of like nature, it might 
be supposed that the non-sexual or agamic! production of 
Aphides, Cynipide, &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 ; 
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 a, not; and yauos, marriage. 
