ON THE AGAMIC REPRODUCTION AND MORPHOLOGY OF APHIS 33 
the following propositions may be said to be established on good 
evidence :— 
1. Ova deposited by impregnated female Apfzdes 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 unfor- 
tunately in diametrical contradiction to one another as to the most 
important points. 
Professor 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 promulgated in Siebold and 
Kolliker’s Zeitschrift for 1850, vol. 11. 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” (/¢. 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 Ap/zs 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 between the 
agamic germ in its youngest state and a true ovum at a corresponding 
period. 
Von Siebold implies, and Professor Owen, Victor Carus, and the 
1 See Hausmann’s ‘‘ Beitrage” in Illiger’s Magazin, Bd. 2. 
VOL. II D 
