THE MOSQUITO 93 



mittent strokes and rests at the bottom of 

 the water. Its own buoyancy brings it back 

 to the surface, as, unHke the larva, it is Hghter 

 than water. Not only has it a certain amount 

 of air in its tracheae, but there is a reservoir 

 of air at the posterior end of the thorax 

 which acts as a very efficient float. When 



Fig. 24. — a. Side view, b, ventral view, of the 

 pupa of a male Anopheles macuKpennis ; o and D, 

 the same views of the female pupa. 



retreating below the surface the respiratory 

 trumpets usually carry down with them two 

 minute air-bubbles. 



The sex of the pupa can be determined 

 by the lobes at the posterior end of the tail : 

 A and B (Fig. 24) representing the male, and 

 c and D the corresponding parts of the female. 

 The duration of the pupal life is generally 

 three to four days, but conditions of temperature 

 and the state of the natural surroundings 

 exert considerable influence upon the rate 



