INSECTS 



355 



fringed hind-legs, row themselves along upon their backs. Like 

 the forms already mentioned, they prey upon small flies and the 

 like. 



Order 2. FRINGE-WINGED INSECTS (Thysanoptera) 



This is a very restricted order, including minute insects with 

 suctorial mouth, long narrow body, well-developed slender an- 

 tennae, and four narrow wings 

 with a fringe of hairs. The 

 male is wingless. There 



s 



also a peculiarity about the 

 feet, which end in bladder-like 

 lobes. 



Some of the species infest 

 flowers, e.g. those of Elder; 

 and the Corn Thrips ( Thrips 

 cerealiitm] (fig. 206) does 



/ V o / tig. 200. Lorn I hnps (Tnrtps cereahum); i, 2, female walk- 



deal of damaP~e tO * n ; 3' 4 ' fe ma ^ e flying- Potato Thrips (Thrips minutissima}; 



5, 6, larva; 7, 8, female flying; 2, 3, 5, 7, natural size; i, 4, 6, 8, 



enlarged. 



Order 3. FLIES (Diptera) 



This is one of the largest orders of Insects, and includes not 

 only innumerable Flies, but also those modified forms which are 

 known as Fleas. As the scientific name indicates (Gk. dis, twice; 

 pteron, a wing), only two wings are present (fig. 207). These 

 are membranous, with comparatively few nervures, most of which 

 run longitudinally, and they correspond to the fore-wings of other 

 Insects. The hind- wings, however, have not entirely disappeared, 

 but are represented by two club-shaped vestiges, which from their 

 function are known as balancers (halteres\ 



The mouth-parts (fig. 207) are adapted for sucking, and often 

 for piercing as well, but there are considerable differences from 

 the arrangements which serve similar purposes in the Hemiptera. 

 These structures are best developed in the females of such forms 

 as Gnats, Mosquitoes, and Gad- Flies, where mandibles, maxillae, 

 and tongue are in the form of five piercing stylets, ensheathed 

 in an imperfect tube formed by the labium and partly covered 

 over by the long sharp labrum. Maxillary palps can be seen 

 at the base of the proboscis. In the males of these forms, and 

 both sexes of some members of the group, e.g. House- Fly (Musca 



