206 



SYSTEMATIC ZOOLOGY 



head, another the other hairy portions of the body, and the 

 third the skin, particularly of the chest and back. This last is 

 interesting because of the variation in color which it exhibits 



according to the color of the skin of 

 its host ; thus on the European it is 

 whitish, on the Chinaman yellowish, 

 on the African black, and so on. Lice 

 very similar to these, but placed in 

 another genus, may infest all the 

 domestic animals. 



The second group, having the wings 

 of uniform thickness, is further dis- 

 tinguished by the absence of a neck, 

 the thorax and head being closely 

 approximated. To this group belong 

 the scale insects and mealy bugs, 

 which are such a pest in green- 

 houses, and in warm regions to out- 

 of-door vegetation as well (Fig. 204). These are small insects; 

 the male is usually provided with a single pair of thin, mem- 

 branous wings, the female is wingless and the body scalelike 

 or gall-like. Some of these insects, however, are of considerable 



Fir,. 204. Coccus cacti, the cochi- 

 neal insect of Mexico, a, female; 

 b, male. (Alter Burmeister, from 

 Clans and Sedgwick's Text-book.) 



Fig. 205. Aphis rosce and larva. 1 From Cuvier's Animal Kingdom.) 



commercial importance, such as the cochineal insect, Coccus 

 cacti (Fig. 204); this is a native of Mexico, but is now cultivated 

 in many other countries, and from the dried adult females 

 cochineal is obtained. Shellac and China wax are also prepared 

 from substances formed by similar insects. The plant lice or 



