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 I'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 (feve) to eleven, which was one 

 more than Bonnet had obtained. The process lasted seven months, and the last young 

 was bom 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- 

 peratm-e on the fecimdity of the viviparous Aphis. 



•It is in Morren's in many respects valuable paper on the Aphis Persicce, 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 occiu's* : — 



" 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 larvae alone are produced." 



Morren here supposes liimself 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 E.^aumui', Bonnet, Degeerf, 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 Ms 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 Fersicte," says he, "I have very frequently 

 seen (and I have shown the phenomenon to my colleague, M. Burgraeve) that the winged 

 and fertiUzable female never contained ova and never laid any, but that she contained 

 little living Aphides, which are born fuUy developed, and provided with legs, proboscis, and 



* " L'influence de la temperature sur ces animaux est manifeste ; chez les autres pucerons, et dans les circonstances 

 ordinaires, la femelle pond des oeufs lorsqu'elle est ailt'e, et apres un accouplement avec le male aile a la meme epoque. 

 Cette ponte se fait aiusi a la scptieme geue'ration pour les uns, a la neu^ieme ou meme k la onzi^me pour les autres ; 

 avant elle, il y a seulement naissance de femelles naissant a I'^tat de larres." — Morren, /. c. 



f Degeer's account of the gall-forming Pucerou du Pin is an apparent exception to this statement, but I believi- 

 only an apparent one. Degeer expressly states that he never saw the winged form of this species in copulation ; and, 

 besides, it is not a true Aphis at all. 



VOL. XXII. 2 D 



