82 Dr. Burnett on the Development of Viviparous Aphides. 



stances may be exercised, according to Bonnet*, at least through 

 nine generations, while Duvauf obtained thus eleven generations 

 in seven months, his experiments being curtailed at this stage, 

 not by a failure of the reproductive power, but by the approach 

 of winter which killed his specimens ; and Kyber J even observed 

 that a colony of Aphis dianthi which had been brought into a 

 constantly heated room, continued to propagate for four years, in 

 this manner, without the intervention of males, and even in this 

 instance it remains to be proved how much longer these pheno- 

 mena might have been continued. 



The singularity of these results led to much incredulity as to 

 their authenticity, and on this account the experiments were often 

 and carefully repeated ; and there can now be no doubt that the 

 virgin Aphis reproduces her kind, a phenomenon which may be 

 continued almost indefinitely, ending finally in the appearance of 

 individuals of distinct male and female sex, which lay the founda- 

 tion of new colonies in the manner just described §. 



The question arises, what interpretation is to be put upon these 

 almost anomalous phenomena ? Many explanations have been 

 offered by various naturalists and physiologists, but most of them 

 have been as unsatisfactory as they have been forced, and were 

 admissible only by the acceptance in physiology of quite new 

 features. 



As the criticism I intend to offer upon some of these opinions 

 will be better understood after the detail of my own researches, 

 I will reserve their future notice until the concluding part of this 

 paper. 



My observations were made upon one of the largest species of 

 Aphis with which I am acquainted, the Aphis Caryce of Har- 

 ris || . While in Georgia, this last spring, it was my good fortune 

 that myriads of these destroyers appeared on a hickory which 

 grew near the house in which I lived. The number of broods on 

 this tree did not exceed three, for with the third series their num- 

 bers were so great that their source of subsistence failed and they 

 gradually disappeared from starvation. The individuals of each 



* Traite d'lusectologie, ou Observations sur les Pucerons, 1/45. 



t Mem. du Mus. d'Hist. Nat. xiii. p. 126. 



X Germar's Magaz. d. Entomol., 1812. 



§ For details of experiments by which Bonnet's original results were 

 verified, see Reaumur, Memoires, iii. Mem. 9 and 11, and vi. Mem. 13. 

 Also, DeGeer, Memoires, iii. ch. 2, 3. Curtis, Trans. Linn. Soc. vi. ; Philos. 

 Trans. 1771- Sauvages, Journ. de Physique, i. Dutrochet, Memoires, ii. 

 p. 442. See also the more modern writers, and especially Kirby and Spence, 

 Introduction to Entomology, iv. p. 161. 



|| A Treatise on some of the Insects of New England which are injurious 

 to Vegetation, 2nd ed. 1852, p. 208. As Dr. Harris says, it is probably 

 Lachnus of Illiger (Cinara of Curtis). 



