4488 Insects. 



are then repeated, and so on almost indefinitely, experiments having 

 shown that this power of reproduction under such circumstances 

 may be exercised, according to Bonnet, at least through nine genera- 

 tions, while Diivau 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 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 phenomena 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 care- 

 fully 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 foundation 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 ad- 

 missible 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 Caryae of Harris. 

 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 numbers were so great that their 

 source of subsistence failed, and they gradually disappeared from 

 starvation. The individuals of each brood were, throughout, of the 

 producing kind, no males having been found upon the closest search ; 

 they were all, moreover, winged ; and those few that were seen with- 

 out these appendages appear to have lost them by accident. I men- 

 tion this fact especially, since it has been supposed by naturalists 

 that the females were always wingless, and therefore that the winged 

 individuals or the males appeared only in the autumn. 



The first brood, upon their appearance from their winter hiding 



