35 [455] 



The incipient galls of the species now under consideration can be de- 

 tected early in May, and by the middle of this month they are visible at 

 a distance on account of their reddish tint. la the early part of the 

 season each gall is occupied by a single, wingless, female aphis, which, 

 by midsummer, becomes the mother of a numerous progeny, often 

 amounting to one hundred and fifty in number. From the very small 

 and tender condition in which this insect is lirst seen in the spring, not 

 exceeding at this time the twentieth of an inch in length, it is probable 

 that it passes the winter in the egg state, which is known to be the case 

 A\ith the Aphides generally. Upon examining the twigs of the Cotton- 

 wood with a lens, late in the fall, I have detected a small number of 

 black eggs, about the fortieth of an inch in length, imbedded in the lit- 

 tle folds at tlie base of the buds. As the eggs of some other species of 

 Aphides are known to be deposited in similar situations, and to have 

 the same black color, it is not improbable tliat these may be the eggs 

 in question. The only circumstance which threw a doubt upon this 

 point, was the very small number of these eggs that I could dis(i0ver in 

 comparison with the ordhiary profusion of galls. 



Judging from what is known of other species of Aphides whose his- 

 tory has been more continuously studied, we may conclude that the eggs, 

 by means of which these insects are perpetuated through the winter, 

 are deposited by the last brood of impregnated females, latp in the sea- 

 son. Strange to relate, these eggs produce fertile females, which in 

 due time, produce liWng young, without having had any union with the 

 other sex, and this process is capable of being continued through a 

 number of successive generations. Ordinarily, and perhaps always, in 

 the state of nature, male indi^^duals are produced before the close of 

 the season ; but the experiments of Kyber, as quoted by Westwood, 

 show that under certain artificial conditions, this process of reproduc- 

 tion without the male influence, may be continued through a inindjer of 

 years. 



The facts observed in the life history of the gall-making Aphis of the 

 I>oplar leaf, render it altogether probable that this species is propagated 

 essentially in the same manner. We uniformly find in these galls, in 

 their incipient stages, a solitary wingless individual which, later in the 

 season, becomes greatly distended, and in due time is found surrounded 

 with a numerous progeny. We have never discovered any eggs of the 

 Aphis in the cells, nor have we been able to detect any distinctly formed 

 ova in the bodies of the distended females, from which we conclude 

 that, like many other species of Aphides, they bring forth their young 

 alive. 



The young lice are of a pale-greenish color, with the tips of their ab- 

 domens covered with a cottony secretion. By the first of June some of 



