ARTHROPODA. 



297 



The posterior pair is very much reduced or wanting. The mouth parts 

 are well adapted for piercing and sucking. The order is very large in 

 species and includes such common forms as the flies, mosquitoes, gnats, 

 fleas. Many members of this group are of great importance to man. The 

 maggots of the true flies are scavengers, developing in decaying organic 

 matter and assisting in its destruction; the adults, on the other hand, 



FIG. 140. 



. l r rc. 140. Stages in the development of the Bot-fly (Gastrophilus equi). From 

 Parker and Haswell, after Brehm. a, adult insect; b, egg attached to a hair; c.d. and e, 

 stages in the development of the larva. (See also Fig. 139.) 



besides being unpleasant companions and demanding a share of our com- 

 forts, probably spread disease. Other species suck the blood of man and 

 domestic animals, producing disease and death. The bot-flies are most 

 important in their larval stage. The eggs, deposited on the exterior, are 

 taken into the digestive tract and there develop, often migrating into 

 other organs and producing definite diseases. Mosquito larvae devour the 

 decaying organic matter in stagnant pools. The adult, especially the female, 

 is a blood-sucker and is, through the parasitic protozoa which may infest 

 it, the chief instrument of the spread of malaria and yellow fever among 

 men. They are all very prolific and develop rapidly considering the fact 



