IV. INSECTA: HEXAPODA, DIPTERA. 491 



.arous females are wingless. At times winged females appear and spread 



2 



FIG. 528. Phylloxera vastatrix. (From Ludwig - Leunis.) 1, winged generation; 

 2, grape root, with nodosities (a) caused by Phylloxera ; #, wingless root-generation. 



the pests. Winged males appear in the autumn, and the fertilized eggs 

 endure the winter. Of all the species none 

 is more injurious than the Phylloxera vasta- 

 trix * of the grape, which with us does slight 

 damage, but in Europe has destroyed whole 

 vineyards. This is one of our returns for the 

 many pests the Old World has sent us. 



Sub Order III. APTEKA. Wingless bugs 

 with direct development, commonly known 

 as lice, of which three species attack man, 

 one living in the hair (Pediculus capitis*), 

 the others (P. vestimentorum * and Phthirius FIG. 52d.Phthirtus 



inguinalis*) upon the body, 

 live on other mammals. 



Other species 



crab louse. (After Leuckart.) 



Order IX. Diptera. 



Like the Rhynchota, the Diptera, or flies, are sucking insects, 

 but the sucking tube or haustellum is different, here consisting 

 of a tube formed of both labium and labrum, and containing 

 stylets which include, besides mandibles and maxillae (often rudi- 

 mentary), the hypopharynx (fig. 488), the maxillary palpi being 

 present. Only the anterior wings (hence Diptera) are well de- 

 veloped, the hinder wings being replaced by the halteres or bal- 

 ancers, small drumstick-like structures richly supplied with nerves 

 and functioning as organs of equilibration. The thorax is, as in 



