198 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 
When the natural history of the Aphides is freed from the mythical additions which 
have accumulated around, and obscured it, I believe the following propositions may be 
said to be established on good evidence :— 
1. Ova deposited by impregnated female Aphides in autumn are hatched in the spring. 
2. From these ova, viviparous, and in the great majority of cases apterous, forms 
proceed. 
3. The broods to which these give rise are either winged or apterous, or both. - 
4. The number of successive broods has no certain limit, but is, so far as we know at 
present, controlled only by temperature and the supply of food. 
5. On the setting in of cold weather, or in some cases on the failure of nourishment*, 
the weather being still warm, males and oviparous females are produced. 
6. The males may be either winged or apterous. 
7. So far as I am aware, there is no proof of the existence of any exception to the law 
that the oviparous female is apterous. 
8. Viviparous Aphides may hybernate, and may co-exist with oviparous females of the 
same species. 
So much by way of clearing the ground. I now proceed to the particular subject of 
this paper, which is primarily, to describe the nature of the process by which the agamic 
young arises within the body of its viviparous parent. But very few investigators have 
applied themselves to this question, and those who have are unfortunately in diametrieal 
contradiction to one another as to the most important points. 
Prof. Leydig published a notice on this subject in the ‘Isis’ for 1848, which I have 
not seen ; but subsequently his views, fully stated and accompanied by figures, were pro- 
mulgated in Siebold and Kölliker's Zeitschrift for 1850, vol. ii. Heft 1. He maintains 
“that the germ of the (viviparous) Aphis is developed out of cells, and its embryo is as 
much composed of cells as one which has proceeded from a fecundated ovum” (1. c. p. 65). 
And he particularly details the manner in which one of the large cells contained in the 
terminal chamber of the proliferous organ of the viviparous Aphis becomes detached, 
enlarges, and is converted into the embryo. Although Leydig does not absolutely say as 
much, his observations lead to the conclusion that there is no histological difference be- 
tween the agamic germ in its youngest state, and a true ovum at a corresponding period. 
Von Siebold implies, and Prof. Owen, Victor Carus, and the late Dr. Waldo Burnett 
assert, with different degrees of distinctness, on the contrary, that there is a clear histolo- 
d i i LE] y 
me ten ee I have carefully, and more than once, scrutinized this volume of the ‘Annales, 
vel of RER = to discover the passage referred to. Léon Dufour has, in fact, two memoirs in the first 
of the ‘Annales’ for 1844. The first is on the « Anatomie générale des Diptères ;” the second, “ Histoire 
des Métamorphoses et de I Anatomie du Pioph a ei xpected there 18 no 
il P t 
asionis, As might be € » 
r ær Royale des Sciences, 1703), however, and I find only this: 
m É d Hi * a em 
Bets vis es ke que les pucerons vivent une année entière, et que pendant l'hiver ils se retirent dans des trous, 
== nt au printems pour pondre leurs œufs, comme le font les mouches ordinaires.” 
Hausmann's “ Beiträge” in Illiger's Magazin, Bd. 2. 
