78 ZOOLOGY 



domesticated animals. In our climate the Diptera occur 

 chiefly in houses, staljles, and among animals, where the 

 highest temperatures are to ))e found. 



The larva? of some Diptera live in the water, but others dwell 

 in decaying matter. Indeed, some Idncls feed exclusively 

 upon horse manure and upon other kinds of filth, and others 

 feed upon our foodstuffs. The larva? that li\-e in deca5Tng 

 matter arc slender without even an enlargement for the head 

 or«dth any especial organs around the mouth, since they have 

 only to suck the fluids in which they develop. In accordance 

 with their structure and habitat we find them lox-ing moisture, 

 darkness, a high temperature, and contact. The latter instinct 

 leads them to penetrate into the material in which they breed. 

 JNIan}' eggs are laid by each female parent, and their de^-elop- 

 ment is very rapid ; indeed, many generations are produced 

 in a single summer. 



The imagos, unlike the larva?, live a free life and, for the 

 most part, in the bright sunshine. They have only a single 

 pair of TOngs, but thej' are powerful flyers and are thus well 

 fitted for their hideous work in disseminating diseases. Their 

 mouth parts are usualh^ pro\dded with a small, dagger-like 

 organ with which they pierce the skin. Through the opening 

 thus formed they suck the blood of their victim. If the victim 

 is diseased, the Diptera become thus inoculated -with the disease, 

 and when they pass to a healthy animal and puncture its skin, 

 some of the disease germs may be inserted into the body of the 

 healthy indi^-idual. In this way mosquitoes cause malaria 

 and yellow fever to spread. 



The method of transportation of disease germs described in 

 the above paragraph, although the commonest, is not the 

 exclusive method. Wherever flies that have developed in 



