300 



ZOOLOGY 



beetles, which are often called "bugs." See Fig. 140. The Hemiptera furnish 

 some really serious pests, as the scale insects, aphids, chinch bugs, etc. 



Order Diptera (two wings}. These Hexapoda undergo a complete metamor- 

 phosis, having the anterior pair of wings developed (not in fleas). 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, besides being unpleasant companions and demanding a share of our com- 



FIG. 141. 



FIG. 141. Larv ae of the Bot-fly (Gastrophilus equf) in the stomach of the horse. One-half natural 

 size. From Luggar, after Heller. 



Questions on the figure. What do you 'know of the habits of the bot-fly? 

 Where are the eggs deposited? How do the larvae come to have the position 

 figured above? How do they pass from this to the adult condition? See also 

 Fig. 142. How does it retain its position in the stomach of its host? 



forts, 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 

 that they undergo a metamorphosis. The fly, for example only requires a few 



