338 



A COURSE ON ZOOLOGY. 



FIG. 302. 



held horizontally at rest, or even folded around the body. 

 The color is generally dark, and the chrysalis is enclosed 

 in a cocoon. This group is numerous, and some species 

 do much damage, the larvae eating woollen and other 

 fabrics. 



Mimicry, or imitation of surrounding objects, is often 

 exhibited to a remarkable degree in the lepidoptera ; the 

 leaf-butterfly (Fig. 301) is almost indistinguishable from 

 a brown leaf as it rests upon a branch or twig. 



The diptera have only one pair of wings, the missing 



pair being usually replaced 

 by two movable append- 

 ages, called balancers. The 

 mouth is organized for 

 suction ; sometimes, as in 

 the fly, it consists of a 

 simple fleshy and retractile 

 proboscis, whose free ex- 

 tremity acts as a sucker; 

 sometimes, as in the mos- 

 quito, there is a cylindri- 

 cal sheath containing five 

 scaly darts, each of which 

 ends in a sharp point flat- 

 tened like a lance. The 

 'metamorphosis of the dip- 

 tera is generally complete. 

 The larvae are usually with- 

 out limbs, and are com- 

 monly called worms. They 

 are born and pass the first 

 stage of their life in stagnant waters or moist soil or 

 among rotten matters. Many species are ovoviviparous. 



LIFE-HISTORY OF THE GNAT (Culex 

 pipiens).a, larva ; b, pupa ; c, per- 

 fect insect emerging ; d, male, and 

 e, female gnat. 



