AND MORPHOLOGY OF APHIS. 195 
females, and that the energy of the power of agamic reproduction was at the end of that 
period undiminished. The rapidity of the agamic prolification throughout the whole 
period was directly proportional to the amount of warmth and food supplied. 
Duvau, in his already cited “Nouvelles Recherches sur l'histoire naturelle des Pucerons,” 
read before the French Academy of Sciences in 1825, states that he had carried the series of 
successive agamic generations in the Aphis of the Bean (fève) to eleven, which was one 
more than Bonnet had obtained. The process lasted seven months, and the last young 
was born on the 27th December, but died on the 29th. Duvau, however, kept some alive 
until January, and naturally asks whether it is not probable that, under favourable cir- 
cumstances, the agamic process may be continued throughout the winter. The average 
length of life of his Aphides was thirty days, or a little more; but the representative of 
the ninth generation lived from September 29th to December 19th, or eighty-one days. 
Like those of preceding observers, Duvau's researches clearly show the influence of tem- 
perature on the fecundity of the viviparous Aphis. 
It is in Morren's in many respects valuable paper on the Aphis Persice, published 
in the ‘Annales des Sciences Naturelles’ for 1836, that the germs of the two most 
notable errors which have crept into the natural history of the Aphides may be found. 
At p. 76 the following passage occurs* :— 
“The influence of temperature on these animals is obvious; in other Aphides, and 
under ordinary circumstances, the female lays her eggs when she has wings and after 
copulation with the male, who is winged at the same epoch. Oviposition takes place in 
this manner at the seventh generation for some—at the ninth or even at the eleventh for 
_ others; before it, female larvæ alone are produced.” 
. Morren here supposes himself to be simply repeating what he has read. But so far 
as I am acquainted with the older literature of the Aphides, he is entirely mistaken. I 
can nowhere discover that either Réaumur, Bonnet, Degeert, Kyber, or Duvau have 
. Observed winged oviparous females in any species; nor do the statements of any of these 
observers justify the belief that the sexual forms always appear after a certain number of 
generations. All that Bonnet affirms is, that his particular experiments came to an end 
accidentally after the production of a certain number of agamic generations, which is, of 
course, quite another matter. ‘ 
- When Morren details his own observations, his results are in exact accordance with 
those of the older observers. “In the Aphis Persice,” says he, “ I have very frequently 
seen (and I have shown the phenomenon to my colleague, M. Burgraeve) that the winged 
and fertilizable female never contained ova and never laid any, but that she contained 
little living Aphides, which are born fully developed, and provided with legs, proboscis, and 
* « L'influence de la température sur ces animaux est manifeste ; chez les autres tage et — V. rer Y 
ordinaires, la femelle pond des œufs lorsqu’elle est ailée, et après un accouplement e le mále nde t ^tm à 
Cette ponte se fait ainsi à la septième génération pour les uns, å la neuvième ou même å la onzième pour les i 
avant elle, il y a seulement naissance de femelles naissant à l'état de larves."—Morren, l. å Gd T belies 
T Degeer's account of the gall-forming Puceron du Pin is an en — m - - ard a: daté m 
only an apparent one. Degeer expressly states that he never saw the winged form of this species in cop ER 
besides, it is not a true Aphis at all. , 4p 
VOL, XXIF 
