HEMIPTERA. 



173 



Scale and of the Red Scale of the Orange ; and it may be seen 

 at the smaller end of the scale of the Oyster-shell Bark-louse. 

 The position of this cast skin in the scale differs in differ- 

 ent genera, and forms a good character for classification. 



Closely allied species differ but little in the form of the 

 scale. To distinguish these it is necessary to study the 



FIG. 213. Aspidiotus aurantii : scales on leaves of orange, natural size; in, adult male- 

 much enlarged ; ib, scale of female enlarged; ic, scale of male, enlarged. 



insects themselves, which are found beneath the scales 

 The distinctions between closely allied species are such, 

 that it requires very close observation and much skill in this 

 particular line to make the determinations, a careful prepa- 

 ration of the specimens and an excellent microscope being 

 necessary requisites. 



The different species of scale-insects vary as regards their 

 food habits. We find that certain species infest particular 



