368 



INVERTEBRATES. 



of the plant's weakness, but the sign ; however, by wounding and 

 sucking the leaf, they increase the disease. They generally assume 

 their color from the plant on which they reside. Those that feed 

 upon pot-herbs and plum-trees, are of an ash-color, only they are 

 greenish when they are young : those that belong to the alder and 

 cherry-tree are black ; as also those upon beans, and some other 

 plants: those on the leaves of apples and rose-trees are white, bat 

 as they leap, like grasshoppers, some place them in the number 

 of the flea kind. The most uncommon 

 color' is reddish, and liee of this sort may 

 be found on the leaves of tansey ; and their 

 juice, when rubbed in the hands, tinges 

 them with no disagreeable red. All these 

 live upon their respective plant, and are 

 often engendered within the very substance 

 of the leaf. 



The Scale Insect is also very 

 injurious to plants, living on the sap, and 

 depositing its eggs on the bark. The 

 cochineal of commerce is a scale insect. 

 The vine-scale insect forms a longish, 

 marbled-brown scale. In old age, the scale 

 ■ becomes blackish-brown, hemispherical and 

 wrinkled. The eggs, which are laid under 

 the body of the female, are covered with long white wool. They 

 are found on vines, particularly in gardens. 



The Scale Insect. 



III. — SCALE-WINGED INSECTS. 



This order is divided into butterflies and moths ; the first 

 of which fly in the daytime, and the latter only at night. They 

 are all provided with four wings, and all pass through a complete 

 series of metamorphoses. Their larvae, known under the name of 

 worms or caterpillars, spin webs for their covering while in the 

 chrysalis state. The silk of commerce is prepared from the web 

 spun by the silkworm for its residence during this dormant state 

 of existence. 



