194 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 
and experiment, and they have been confirmed by every subsequent original observer 
whose works I have perused. Besides these matters of fact, Bonnet states, as his strong 
opinion, that there is no fixed limit to the process of agamic, viviparous reproduction, and 
that, under favourable conditions of warmth and nourishment, it might be continued for 
* thirty generations" (Z. c. p. 102), or, in other words, indefinitely. 
The accurate and pains-taking Degeer, who gives an elaborate account of some seven- 
teen species of Aphis, affirms as the result of his researches, “that the winged Aphides 
are never oviparous*." He describes at length the apterous males of certain species 
(P. lisse du Pin, P. du Pommier, P. du Genévrier), and shows that apterous, oviparous, 
and winged viviparous broods may coexist, as in Aphis Rose. 
Degeer considers that, as a general rule, the oviparous females and the males are pro- 
duced by alate viviparous females. 
The next important original memoir on the Aphides is that published in Germar's 
Magazin der Entomologie for 1815, by Kybert, evidently a most careful observer, but 
somewhat wanting in method and clearness as a writer. Kyber is in perfect accordance 
with Bonnet and Degeer; and more than this, he experimentally proved the justice of 
Bonnet's supposition, that the duration of the agamie reproductive power is practically 
indefinite, and is chiefly, if not wholly, dependent on conditions of temperature and 
- nutrition. He says (p. 34) :— 
*I never saw a male in copulation with a winged female in any species. It was 
always the apterous females which were attacked by the males; for in many species apte- | 
rous females remain among the families. Neither have I ever seen winged females lay 
eggs. This has, indeed, been already remarked by Degeer.” 
_ Ina note Kyber adds the caution, that he has not observed more than twenty species 
in copulation, and does not wish to extend his conclusions beyond these. 
The fourth note to this important paper contains the following remarkable observation : 
—......“ The winged females especially, in which, even after frost has set in, fully-formed 
young may always be found, when the apterous females of the same family have long 
been laying eggs. On the 21st November, 1812, I still had winged Aphides (Haberblatt- 
låuse) in my possession, although the apterous ones had copulated and laid their eggs in 
September, —a remarkable circumstance without doubt, and one whence important con- - 
clusions with regard to the mode of propagation of the Aphides are likely to flow. Pos- 
sibly, many winged females survive the winter together with their young.” (p. 10.) 
In other parts of his memoir (p. 2 et seq.), Kyber adduces strong evidence in favour of 
the hybernation of the viviparous forms of some species; which Degeer had already 
proved to be the case with respect to the remarkable * Puceron des Galles du Sapin.” 
5 the Aphis Dianthi, Kyber was never able to observe either copulation or oviposition ; 
a nn being any natural term to the number of asexual broods which. 
an ie = T that he raised viviparous broods of both this species and 
: ecutive years, without any intervention of males or oviparous 
* Degeer, Mém. sur les Insectes, 1774, vol. iii. p. 74. 
t v Erfahrungen und Bemerkungen über Blattliuse von J. F. Kyber, Diacon. in Eisenberg. 
