SCALE INSECTS 53 



The true scale insects 1 constitute the series Mono- 

 mera of the Homoptera. They are minute insects 

 whose tarsi have only one joint, terminating in a single 

 claw. A common species is the mussel-scale, 2 which 

 may often be found thickly encrusting the twigs of 

 apple, hawthorn, and other trees and shrubs. If, in 

 autumn, one of the larger scales be carefully lifted 

 with the point of a needle, and examined under a lens, 

 it will be found to contain the shrivelled body of 

 the female insect, together with from 50 to 100 

 eggs. The newly hatched larva, which escapes from 

 the scale in the spring, is an active, six-legged 

 creature. It settles down upon a twig, from which it 

 sucks the sap, and at the same time begins to secrete 

 its scale. The latter grows with its owner, forming 

 an effective shield or cover comparable to the shell of 

 a limpet. The developing scale insect remains con- 

 stantly in one spot, anchored by its proboscis. Indeed, 

 the adult female a grub-like creature, destitute of 

 wings and legs never leaves her scale at all. The 

 male larva, however, becomes quite passive prior to 

 its final moult, and assumes a state closely approach- 

 ing to the true pupa of the higher orders. It is 

 eventually transformed into a winged insect with long 

 antennae and well-developed legs ; but only its fore- 

 wings are functional, while its mouth-parts are reduced 

 to mere useless vestiges. The males appear when 

 the females are almost ready for oviposition ; but they 

 are rare, and parthenogenesis probably prevails. The 

 family Coccidcz includes numerous species, which are 

 attached to many kinds of plants. All do not form 

 scales. The felted beech coccus, 3 for example, lives 

 gregariously beneath a white, flossy substance, in the 

 2 Mytilaspis pomorum. 3 Cryptococcus fagi . 



