48 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



present on the third antennal segment, in apterous adults (fig.r), 

 while in the alate insects this segment bears from four to eight 

 of these sensoria, both the average and the mean being six (fig. ri) . 

 These sensoria are large and generally of uniform size. More- 

 over, in the vast majority of cases, the numbers on the two an- 

 tennae are equal. In nine intermediates, this segment bore from 

 four to six sensoria, the average being slightly under five per 

 antenna and the mean, four. In seven out of the nine cases 

 the numbers on the two antennae were not equal. Moreover, 

 these sensoria were very unequal in size. In some cases they 

 were all large, though never as large as in alate insects, in some 

 small, while in still others they varied greatly in size, the dis- 

 tribution of the small ones also varying (figs. o-q). 



This form occurred in sixteen different experiments with a 

 known total of thirty individuals. The first occurrence was in 

 the third generation, on May 29, and the last in the twelfth 

 generation, on August 26. It occurred in at least one experi- 

 ment in all of the intervening generations, with the exception of 

 the fourth and ninth. Of these sixteen lots, thirteen were pro- 

 duced by apterous mothers and three by alate. In only two 

 cases did intermediates occur without the presence of alate 

 sisters. 



Eleven of these series reproduced normally, the other five dying 

 before reproduction took place. All eleven series produced apter- 

 ous offspring and three of them also produced alate forms. In 

 two cases single individuals brought forth progeny, some of which 

 became apterous and some alate-. This polymorphic reproduc- 

 tion is of quite common occurrence in this species among both 

 alate and apterous mothers. All of the young were perfectly 

 normal and in several cases we were able to carry the descendants 

 through several generations (in the case of the earliest through 

 thirteen) to the sexual forms. 



In 1912 Webster and Phillips recorded the occurrence of a 

 similar form produced under similar conditions in Toxoptero 

 graminum, a species in which, also, the majority of the summer 

 form are apterous, but in which alate individuals occur quite 

 frequently. They stated that they observed one instance in 

 which a puparium produced six young. Apparently they did 

 not rear these young. The note continues. "The cauda of 

 this individual resembled that of an adult insect and the wing 

 pads were aborted, the abdomen being much broader than that 

 of the normal pupa." 



Through the kindness of Professor Webster, we have since 

 examined this specimen (mounted on a slide) and find it to 

 correspond, as far as reduction is concerned almost exactly to 

 our intermediate. The wing muscles are very much reduced; 



