PURE LINE INHERITANCE AND PARTHENOGENESIS. 2~J 



greatly in their period of longevity and in their fecundity. Some 

 will die in a few days after reaching maturity, and will leave few 

 or no offspring. Others may live for two weeks or more, and 

 leave at least a score of offspring. 



The young when born are quite similar to the adults except 

 in size. They at once begin to feed, and after molting three or 

 four times they reach maturity. Although the immature indi- 

 viduals are quite content to settle on the same stalk next to their 

 mother, and to remain there throughout their period of growth, 

 when they reach maturity, especially if they are winged, they 

 are restless, and generally leave the plant upon which they have 

 been reared. 



VARIATIONS. 



This aphis is quite variable in several respects. Pergande, 

 who has made a special study of the species, states: "I have 

 found a certain range of variation in the comparative length in 

 the joints of the antennae, as well as in the nectaries of the 

 progeny of the apple louse [Aphis avence], the extreme forms of 

 which may easily induce superficial students to consider them 

 as distinct. Large series, however, of the various forms, more 

 or less due to the season or abundance of food, have convinced 

 me that all of them belong to but one species." 



I cannot agree with Pergande in attributing these variations 

 entirely to the season or the food supply. For ten generations 

 I have reared these aphids exclusively on young wheat shoots, 

 and I find that most of these variations obtain even in their 

 extremes when all individuals are reared on the same diet. How- 

 ever, the food supply certainly does affect some of the varia- 

 tions, but most of them originate without a change in the 

 amount or nature of food taken. What is more significant, 

 I find these variations existing among offspring of a single 

 female reared under identical conditions and even find the 

 antenna on one side differing from the antenna on the other 

 side in the same individual. In regard to this latter point, 

 however, I find that for a large majority of the individuals ex- 

 amined the antennae on the two sides of the same individual are 

 the same or nearlv so. 



