PARASITES. 135 



instruments of locomotion, appended to the extremity of their 

 abdomen. (Fig. 141.) The Order includes but two genera, the 

 Sugar-Lice and the Spring-tails. 



The Sugar-Lice (Lepisma)baye a row of filaments attached to the hind- 

 most ring of the body, three of which are of considerable length, and by their 

 assistance the Lepisma leaps into the air. Their legs are short, but they run 

 with great swiftness. Many species of these insects lurk in the chinks of 

 window-sashes that are seldom opened, or they hide under wet planks and 

 in cellars 



The Spring-tails (Poduro) have their tail terminated by two stiff spines, 

 which are usually bent under the body. By suddenly extending this apparatus, 

 which acts as a spring, the insect leaps into the air like a skip-jack, and falls 

 upon its back. The Podurae are found under the bark of trees, or sometimes 

 on the surface of stagnant water, or even of snow. They are generally con- 

 gregated together in considerable numbers, and have very much the appear- 

 ance of grains of gunpowder. 



FIG. 141. ARCTIC SPRING-TAIL. FIG. 142. LOCSE. 



PARASITES. ORDER PARASITA. 



The Parasita are wingless insects that do not undergo meta- 

 morphosis, and whose abdomen is without any terminal appendage 

 (Fig. 142). Their mouth is adapted for suction, their body is flat- 

 tened, and, as their name indicates, they live upon other animals. 

 They are, however, only met with in mammals and birds. They 

 are generally known by the names of 



Lice (Pediculus) and Ticks (Ricinus). The latter, with the exception of 

 the Dog-tick, only infest birds. These insects, by means of prehensile claws 

 with which their feet are armed, cling to the hairs of quadrupeds and the 

 leathers of birds, in which situation they pass their lives, and sometimes 

 multiply very rapidly. They fasten their eggs, which are called nits, to the 

 hairs or feathers upon which they climb. 



