20 Mosquitoes 



catch in the surface film ] and, in conjunction with 

 the breathing tubes, which project through the film, 

 to preserve the balance of the top-heavy pupa. On 

 the various abdominal segments are numerous hairs 

 and tufts, the length, number, and position of which 

 can be utilised as specific characters in conjunction 

 with the tufts on the cephalo-thorax. It is true 

 that they can be seen only with the aid of a com- 

 pound microscope, nevertheless they are present and 

 constant, and it is sometimes better to identify by 

 difficult and minute characteristics than not to dis- 

 tinguish at all. The abdomen ends in two dorso- 

 ventrally flattened paddles, which serve as propellers- 



1 By surface film is meant, not scum, but the film formed by the 

 tension of the water at the point of contact with the air. 



