410 



ZOOLOGY. 



provided with hooks. Sometimes they change the skin 

 times, and spin a cocoon, to transform themselves in it into a 

 nvnijih : at other times they do not moult, and their skin, 

 hardened and horny, becomes for the nymph a solid cocoon, 

 having the appearance of a reed (Fig. 402, a). 



In this division we place, in addition to the flies, properly 

 so called, the gnats, the gad-fly (Fig. 403), the tustrus (Fig. 

 402), &c. 



Fig. 404. Stylops. 



Fig. 405. Pediculus humanus. 



Fig. 406.-Machili8. 



546. The rhipiptera are insects having also but two 

 wings, but in which the organs are folded longitudinally, like a 

 a fan ; two genera only are known, the stylops (Fig. 404) and 

 the xenos, which in their state of larva live as parasites on 

 the abdomen of wasps and other hymenoptera. 



547. The order anoplures or parasites is not numerous, 

 and is composed of insects which are always without wings, 



