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" {I. 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, afiirras 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 Gen^vrier), and shows that apterous, oviparous, 

 and winged viviparous broods may coexist, as in Aphis Roscb. 



Degeer considers that, as a general rule, the oviparous females and the males are pro- 

 duced by alate viviparous fexnales. 



The next important original memoir on the Aphides is that published in Germar's 

 Magazin der Entomologie for 1815, by Kyberf, 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 agamic 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." 



In a 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 foiu'th note to this important paper contains the following remarkable observation : 



— "The winged females especially, in which, even after frost has set in, fully-formed 



youno- may always be found, when the apterous females of the same family have long 

 been laying eggs. On the 21st November, 1812, I stUl had winged Apjhides (Haberblatt- 

 lause) 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 vnth. respect to the remarkable " Puceron des Galles du Sapin." 



In the Aj)his Dianthi, Kyber was never able to oliserve either copulation or oviposition ; 

 and so far from there being any natural term to the number of asexual broods which 

 succeed one another, he states that he raised viviparous broods of both this species and 

 A. Rosw for four consecutive years, without any intervention of males or oviparous 



* Degeer, Mim.. sur les Insectes, 1774, vol. iii. p. 74. 



t Eiaige Erfabrungen unci Bemerkungen iiber Blattlause von J. F. Kyber, Diacon. in Eisenberg. 



