8 



tion. Therefore, the Homoptera are generally believed to be more 

 primitive than the Heteroptera. The Aleyrodidoe and Coccidae 

 represent the highest degree of specialization among the Homoptera* 

 and even surpass the Heteroptera in that both have attained a com- 

 plete metamorphosis. At first glance it appears that the former 

 family, having a complete metamorphosis in both sexes, is a more 

 specialized form than the latter family, but this is more apparent 

 than real. It is in accordance with our belief in regard to the origin 

 of complete metamorphosis that the ancesters of the Coccidae in the 

 adult condition were winged in both sexes, and that the adult form 

 was the result of gradual changes in the immature insects. The 

 Coccid branch, therefore, was derived from the primitive Homoptera 

 with incomplete metamorphosis. In the course of time the younger 

 stages, through the action of natural selection, departed from the 

 original type in which they resembled the adults, as do the other 

 Hemimetabola (insects with incomplete metamorphosis) to-day, so 

 that they approached and finally attained a complete metamorphosis 

 in both sexes. It is not impossible that the degeneration of the 

 female began during the latter part of this process. If this view be 

 correct, the female Coccids have now attained a secondary incom- 

 plete metamorphosis. The male Coccids were evidently prevented 

 from losing their wings by natural selection in order that they might 

 continue to be active in fertilizing the females. Even the adult 

 males are, however, degenerated, having lost their mouth organs, and 

 are so delicately constituted as to live but a few days at the most. 

 The Aleyrodidas have gone through a series of changes similar to 

 those of the Coccidae up to the point where complete metamorphosis 

 was attained, and it is at that point that we find them to-day, although 

 the different species are specialized in various other directions. In 

 tracing the two lines of development backward, beginning with our 

 present forms, do they unite before they reach the primitive Homop- 

 terous branch, or is it simply a case of development along parallel 

 lines owing to the two forms living under similar conditions ? The 

 general resemblance of the two families seems to point to a union of 

 the two lines, although, as a rule, the immature stages of insects are 

 of uncertain value in the study of phylogeny. 



t The Cicadidre attain a high degree of metamorphosis, but it can hardly be con- 

 sidered complete. 



