298 



ZOOLOGY. 



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

 a few hours for hatching into the maggot stage. If food and temperature 

 are favorable, this maggot may grow to full size in a week, when it passes 

 into the resting or pupa stage, from which another week or more is re- 

 quired for the young fly to emerge. 



FIG. 141. Two stages in the metamorphosis of the Mosquito. From Packard. A, 

 larva; B, pupa; C, ventral view of the oar-like appendages of the last segment of the 

 pupa; r, respiratory tube of the larva; r', respiratory tubes of the pupa. 



FIG. 142. 



FIG. 142. The Hessian Fly (Cecidiomya destructor). From Standard Natural His- 

 tory, a, the adult; b, larva; c, pupa; d, larvae in position on stalk of wheat. 



Questions on the figure. Give names to all the structures apparent 

 on the adult. In which stage does the insect do its damage? What is 

 its economic importance? What is the origin of its common name? 



The eggs of mosquitoes are deposited in water, where they hatch into 

 active larvae called " wigglers." These breathe the air by means of a tube 

 on the next to the last abdominal segment. Their common position with 

 the end of the tail at the surface of the water is thus explained. The 



