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 .—Aspidiatus aurantii ; scales on leaves of orange, natural size; m, adult male» 
much enlarged; 1 3 , scale of female enlarged; 1 c, 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 
