IO8 H. E. EWING. 



I only studied the transmissibility of the latter abnormality. 

 Where individuals stopped completely their development in any 

 nymphal stage, they always produced normal young, and in 

 every case these young grew to normal adults. The arresting 

 of the development of these nymphs caused them to become 

 paedogenetic. The paedogenesis, however, was never fixed. 

 Several of these paedogenetic nymphs appeared. Some of them 

 were nymphs of wingless form, and some of the winged form. 

 The cause of the arrested development I did not learn, but it 

 may have been due to low temperatures. 



The variations mentioned in the third discoidal vein are shown 

 in Fig. 18. I hope some time to test the transmissibility of these 

 abnormal wing characters. The variation shown in B is quite 

 common. The variations shown in C and D, on the other hand, 

 are rare. In regard to the variations of this third discoidal vein, 

 it should be mentioned that frequently the venation of the wing 

 on one side of an individual will be different from the venation 

 of the wing on the other side of the same individual. Yet there 

 is a tendency for the anomaly to appear simultaneously on both 

 wings of the same individual. 



THE OCCURRENCE OF PAEDOGENESIS. 1 



The occurrence of psedogenesis (the reproduction parthenogen- 

 etically by immature instars) is a phenomenon known to be well 

 established in the genus Miastor (Fam. Cecidomyiidas), and occurs 

 also in a few of the species of Chironomus. But paedogenesis is 

 extremely rare in the animal kingdom, and as far as the writer 

 can learn has not been recorded as occurring erratically in plant 

 lice. 



In the course of my experiments with Aphis avence, which 

 covered about two and a half years, I observed on several oc- 

 casions individuals that never passed beyond their third or pos- 

 sibly fourth nymphal instar, but nevertheless began and con- 

 tinued to reproduce in a normal manner. These paedogenetic 



1 The word paedogenesis is here used in a broad sense denoting parthenogenetic 

 reproduction by any immature stage of an animal that passes through a meta- 

 morphosis. Nymphal paedogenesis does not have nearly as deep a significance as 

 larval paedogenesis that is found in some insects which pass through a complete 

 metamorphosis. 



