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MANUAL OF ELEMENTARY ZOOLOGY 



batches of 150 eggs, and this, with the shortness of its life- 

 history, enables it, in favourable circumstances, to become 

 immensely numerous. House flies are dangerous pests, 

 because they pick up, from excrement, sputum, etc., the 

 bacilli of typhoid, diarrhoea, tubercle, and other diseases, 

 carry them on their legs and in their alimentary canal, and 

 infect food with them. Blow flies (Calliphora), which lay 

 their eggs in fresh or decaying flesh, including that of 

 open wounds, have a similar life-history. 



7. Aphaniptera. — Jaws for piercing and sucking. No 

 wings. Metamorphosis complete. Fleas. The body of 



ABC 



Fig. 199. — A semi-diagrammatic representation of the way 

 in which bacteria are borne upon the foot of a fly. 



A, the whole foot, showing pads, hooks, and hairs ; 



B, a single hair more highly magnified ; C and C, 

 bacteria. — From Shipley. 



these insects is compressed from side to side (thus in the 

 opposite direction from that of the bed bug), their eyes are 

 small or absent, and their legs very long and strong. They 

 spend part of their time on the body of the host and part 

 on the ground, where they lay their eggs. The larvse have 

 long, narrow bodies, without legs but with bristles by which 

 they pull themselves about actively. They have biting 

 mouth-parts and feed on any kind of organic matter which 

 they find in dust, etc. After about twelve days (in the case 

 of the Human Flea, Pulex irritam) they spin a cocoon and 

 pupate. Various species infest different warm-blooded 

 animals, but many can live for a time on other than their 

 proper hosts. The plague is transmitted by rat fleas. 



