INTRODUCTION 7 



or six inches long as in Takahashia. In certain of the species 

 forming an abundance of wax, it is a thick homogenous mass and 

 in the case of Tachardia, the shellac forming insects, the wax is 

 an important article of commerce. A long time, several weeks 

 to three months, is sometimes required in the production of the 

 ovisac, as in Icerya. The small species may become conspicuous 

 from the large number of individuals present in a given area, 

 this is also increased sometimes by the color, as in the case of the 

 male scales of Chionaspis and Aulacaspis. The number may be 

 so large that the surface is completely covered or encrusted and 

 hence the name of scale insects. Most -of the species that occur in 

 considerable numbers, as the species of Aspidiotus, Lepidosaphes, 

 or Chionaspis, form only a minute leaf-like disk of wax and molted 

 skins. The females of Icerya and of other large species when they 

 are ready to form their large conspicuous ovisacs, seem to con- 

 gregate in the same place so that many adjacent ovisacs are 

 frequently found close together. 



The coccids and aleyrodids of all the insects that undergo 

 a direct or incomplete metamorphosis show the farthest departure 

 from the generalized orthopteran type of metamorphosis. In the 

 case of the Coccidae there is more difference between the two sexes 

 throughout the greater part of their life than exists between many 

 species of insects of other families or orders. 



When the recently emerged coccid is compared with the 

 diagnosis of a typical hemipterous insect and of a gularostrian, 

 it is seen that there is still retained most of the features peculiar 

 to these types. The most striking change is the modification of 

 the compound eyes into a pair of simple eyes or ocellanae, the 

 great reduction in the size of the constrictions between the head 

 and prothorax and the prothorax and mesothorax, the procoria 

 and the mesocoria, so that it is often difficult to determine the 

 limits of the head and of the thoracic segments. The antennae and 

 legs, while they are typical in form so far as segmentation and 

 number of parts are concerned, are different in appearance. They 

 are large and ungainly in appearance and are apparently out of 

 all proportion in size with the remainder of the body. This is not 

 true of other nymphal Hemiptera or of nymphal insects in general. 



The two sexes, while so different throughout the greater part 

 of their life, are indistinguishable during the first nymphal stage. 

 The nymphs, when they emerge from the egg, remain perfectly 

 quiescent for a time, a few hours to two days, in the place where 

 the eggs were laid. These young nymphs are suddenly seized with 



