38 
BRITISH APHIDES. 
Mainly through the repellant action of this meal, 
or down, the subterranean Aphides are enabled to live 
securely in the holes they excavate in soils which are 
often percolated with water. 
Under high magnifying powers this silky secretion 
appears as long flattened fibres, which, when broken 
across, present sharp fractures as if they were brittle 
like glass or asbestos. The fibres are mostly curved, 
and have obscure transverse and longitudinal stria- 
tions. It issues from the glands in dense shining tufts, 
which usually have their tops truncated. This is well 
seen in Amycla and Forda. 
This material is insoluble in water, in alcohol, and 
in solution of potash. It scorches into a brown mass 
over the lamp, without melting ; and gives off, at the 
same time, a nitrogenous odour like burnt feathers. 
This substance, therefore, differs from the secretions 
formed by many other Homoptera, which generally 
are of a waxy nature. For example, this matter is 
abundant on the bodies of some lantern flies, where 
it occurs in filaments exceeding the length of the body. 
It occurs also either in tufts or in a pulverulent form 
amongst the Oicadidge ; those feeding on the thistle or 
nettle roots being most profusely furnished. The 
white flakes often obtained by shaking our box- trees 
proceed from the bodies of Psylla huwi. 
The crystalline, spermaceti-like substance known 
in commerce as Chinese wax is the produce of Coccus 
pela, and Mr. Walker states that a waxy secretion is 
obtained from an Arabian Coccus, which some have 
fancifully supposed might be identical with the manna 
of the wilderness. Thus, individuals of all the insect 
families nearly allied to Aphis cover themselves with 
flocculent matter, of varied constitution, 
A description of the silk glands of Chermes, and the 
peculiar mode in which the silk unravels itself, after 
leaving the pores, will be found in connection with 
Plate C, figs. 6—9. 
Before concluding these observations on the anatomy 
