ARTHROPODA 



301 



which are often called " bugs." See Pig. 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 except in three or four groups, 

 which are wingless. Hind wings reduce;d to mere rudiments. 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. Many members of 

 this group are of great importance to man. The maggots of the true flies are 

 usually scavengers, developing in decaying organic matter and assisting in its 

 destruction; the adults, on the other hand, besides being unpleasant companionsi 



Pig. 141. 



FiG. 141. Larvffi of the Bot-fly {Gastrophitus equi) 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 

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



and demanding a share of our comforts, spread disease. Other species suck the 

 blood of man and domestic animals, producing disease and death.' The bot-flies 

 are most destructive 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 larva; devour the deca,ying organic 

 matter in stagnant pools. The adult 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 aU very prolific and develop 

 rapidly, considering the fact that they undergo a metamorphosis. The house fly, 



