OF WASHINGTON, VOLUME XVII, 1915 49 



the cauda is that of the adult form; and the antennae are armed 

 with sensoria as are the alate adults, there being four on the 

 right and two on the left. 



We have also noted an intermediate in Aphis rutnicis, corre- 

 sponding closely to that in. A. pomi, and in a species of Phylloxera 

 on hickory we have observed one specimen with wings about 

 half the normal size. 



Hunter (1909) and again Webster and Phillips have described 

 forms in T. graminum, which vary between the sexual and par- 

 thenogenetic females. Some of these vary in outward form, 

 between the true female and the alate agamic female; others be- 

 tween the true female and the apterous agamic. Some contain 

 only eggs, others produce both eggs and living young. 



We believe that all of these intermediates are of like value 

 with that which we have found in A. pomi, that is, they all 

 developed toward the alate condition until the end of the third 

 instar, during which stage the pupal form is determined. In 

 the fourth, or pupal instar, however, they tended to progress 

 to the apterous condition. We find no evidence to support Dr. 

 Foa's contention that insects primarily designed to become apter- 

 ous may later tend to become alate, nor can we agree with 

 Borner in his classification of these intermediate forms. The 

 only condition which necessitates such explanations is that in 

 which the intermediates are virginopara, while normal virginopara 

 are apterous. Has not too much stress been laid upon this dis- 

 tinction between virginopar and sexuparse? Dr. Foa, her- 

 self, states that she has observed virgino-sexuparse, which would 

 indicate that the line of demarcation is not strictly drawn, and 

 other authors appear to believe that the intermediate virgino- 

 parse are intermediate in position between virginoparae and 

 sexuparse. 



It is generally accepted that the apterous aphid is a more 

 specialized type, which has been derived from the alate. If 

 this is true, it would seem that the tendency in aphids is to 

 eliminate the wings. At the same time, there would appear a 

 degeneration of secondary alate characters, such as the sensoria 

 on the third antenna! segment, in species like A. pomi. In sup- 

 port of this theory attention is called to the fact that in A. ponti 

 we have been able to breed the insects from the egg stage to the 

 egg stage without the intervention of any alate generations. 



Moreover, the primitive aphids must have been oviparous 

 insects, reproducing sexually. Variations from this type would 

 be the tendency to eliminate males and to transform from ovipara 

 to vivipara. In some species these variations have been followed 

 to their logical conclusions with 'the apparent elimination of both 

 males and oviparous reproduction. In other cases this has been 



