METAZOA INSECTA. 427 



egg develops into a form far removed from its parents 

 and from the ancestral Hemiptera, while the apparently 

 normal sexually mature male and female develop from 

 the unfertilized eggs of agamic individuals. 



The unfertilized eggs may be in a certain sense her- 

 maphroditic, but without going into a discussion l of the 

 subject of parthenogenesis, or the development of living 

 organisms independently of the male, it is evident that 

 the sexually mature male and female which pair and give 

 rise to fertilized eggs are nearer the primitive insects, 

 and also the ancestral forms of nearly all the groups 

 above the Protozoa, than the exceptional agamic forms 

 which bring forth living young. In the latter case 

 acceleration in development has caused the embryonic 

 and larval stages to be passed within the body of the 

 parent, and the young when born may be compared to 

 active pupae which are so specialized . that they never 

 acquire wings, but in a few days are mature insects and 

 ready in their turn to bring forth living Aphides. 



Unfortunately, a figure of the larva of the male Phoro- 

 don cannot be given, but the pupa (PI. 1068, fig. i) has 

 the rudiments of wings like the pupae of most insects. 

 These pupae develop into the male (fig. 2) which has two 

 pairs of wings, although the posterior pair are small in 

 size. The sexually mature female is more specialized 

 than the male, inasmuch as it never possesses wings. 

 Its young, which is probably the specialized wingless 

 pupa, is seen in fig. 3 ; the adult with the body distended 

 with eggs is represented in fig. 4 and with the body 

 shrunken during egg-laying in fig. 5. 



These fertilized eggs are laid upon the branches of 

 plum trees. Each develops into a wingless female often 

 called the "stem mother" (fig. 6), which in a few days 

 produces living young, entirely independent of the male. 

 This second generation (fig. 7) gives rise in the same 



1 See Weismann, Brooks, Geddes, Adler. 



