49° Manual of elementary zoology 



taken at such a rate that much of it passes through the 

 alimentary canal but little altered, and oozes from the 

 hinder opening as a sugary fluid much relished by other 

 insects, especially by ants, which in some cases actually 

 domesticate the aphides in order to obtain it. This fluid, 

 known as " honey dew," was formerly believed to be secreted 

 by a pair of remarkable tubes which project from the fifth 

 abdominal segment. The great plenty of food supports the 

 rapid reproduction by which plantlice withstand the attacks 

 of their many bird and insect enemies. They may be 



Fig. 197. — The Crab Louse (Phthirius inguinalis). — 

 From Sedgwick, after Landois. 



St., Stigma; 7>., trachea. 



destroyed by spraying with various mixtures, containing 

 such substances as paraffin, soft soap, quassia, and tobacco, 

 which are injurious to them in various stages of their lives. 

 6. Diptera, — Jaws for piercing and sucking. Hind 

 wings represented by minute structures known as halteres, 

 having the form of a rod ending in a knob, and probably 

 sensory in function. Fore wings membranous. Meta- 

 morphosis complete. Flies, Gnats and Mosquitoes, Crane- 

 flies, etc We have already had occasion to allude to 

 some of these insects (pp. 149, 156). The House Fly, 

 Musca domestica, differs greatly in build and habits, at all 

 stages of its life-history, from the gnats and mosquitoes, 



