198 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 



When the natiu'al history of the Aphides is freed from the mythical additions which 

 have accumulated aroimd, 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 

 ])roceed. 



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 temperatiire 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 ovii^arous 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. Vi-saparous 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 natvire 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 diametrical 

 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 Kolliker's Zeitschrift for 1850, vol. ii. Heft 1. He maintains 

 " that the germ of the (viviparoiis) 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 detaUs the mamier 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 liistological 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 Cams, and the late Dr. Waldo Burnett 

 assert, with different degrees of distinctness, on the contrary, that there is a clear histolo- 



(les Sciences Naturelles, vol. i. 1844." I have carefully, aud more than once, scrutinized this volume of the ' Annates,' 

 without having been ahle to discover the passage referred to. Leon Dufour has, in fact, two memoirs in the first 

 volume of the 'Aunales' for 1844. The first is on the "Anatomic gencrale des Diptferes ;" the second, " Histoire 

 des Metamorphoses et de rAnatomie du Piophila Petasionis." As might be expected, there is no reference to the 

 Aphides in either of these papers. 



Finally, the authors of the article " Hemipteres " in the ' Suites a Buffon' (1843), p. 600, quote De la Hire as their 

 authority for saying that the oviparous female Aphis is winged. I have examined the passage cited (Histoire de 

 r.\cad. Royale des Sciences, 1/03), however, and I find only this: — 



" M. de la Hire croit que les pucerons vivent une ann& entiere, et que pendant I'hiver ils se retirent dans des trous, 

 d'ou ils sortent au printcms pour pondre leurs ceufs, comme le font les mouches ordinaires." 



* See Hausmann's " Beitriige" in lUiger's Magazin, Bd. 2. 



