METAZOA INSECTA. 419 



united make the labium (fig. 2, d), are very unlike the 

 typical mouth parts although both pairs have palpi (see 

 fig. 2, c, d). According to Osborne, 1 the Thripidae are 

 vegetable feeders, and the carnivorous habit when pres- 

 ent, as in Thrips phylloxerae, is acquired or but recently 

 developed in the species. 



The beautiful wings with their long delicate fringe (PI. 

 1036, Hcliothrips haemorrhoidalis Bouche) have given 

 the name of Thysanoptera or fringe-winged insects to the 

 order. In PI. 1034, fig. 2, these wings are folded over 

 the back. 



The male of Limothrips has become specialized by 

 reduction, having lost its wings altogether (see PI. 1034, 

 fig. 3)- 



Order 9. HEMIPTERA. 



The Hemiptera have probably descended from some 

 Campodea-like ancestor, though many of the stages of 

 descent are wholly skipped in the development of exist- 

 ing forms. Even the most generalized members of the 

 order are far removed, as regards the mouth organs, from 

 the Thysanura and also from the orders so far described. 



While this is true, there are nevertheless certain indi- 

 cations here and there that the sucking apparatus of the 

 Hemiptera, which is so perfect in most of the members 

 of the order, is an adaptation of the original biting mouth 

 parts of the ancestral Thysanura. For instance, in the 

 mouth organs of Zaitha (Z. margineguttata) the second 

 pair of maxillae which form the sucking tube are pro- 

 vided with palpi (PL 1037, fig. i). These have also 

 been seen in Benacus griseus Say (fig. 2), Gerris najas 

 (fig. 3), as well as in Nepa, Ranatra, and Belostoma. 



As we already know, an important feature of biting 



1 U. S. Dep. Agric., Insect Life, I, no. 5, 1888, p. 142. 



