MOSQUITOES AND FLEAS. 



13 



siphon reaches the surface, fresh air flows into its tracheae, and the 



physical properties of the so-called surface film of the water assist it 

 in maintaining its position. 



The account by Miall, in his recently published Natural History of 

 Aquatic Insects, is misleading, for the reason that he assumes that the 

 end of the body, with its four (or, as he has it, five) leaf-like expansions, 

 is the breathing organ. As a matter of fact, as is plainly shown by 

 fig. 2. this end of the body does not reach the surface, and it is the 

 tip of the respiratory siphon only which is extended to the air. This 

 respiratory tube takes its origin from the tip of the eighth abdominal 

 segment, and the very large trachea* can be seen extending to its 

 extremity, where they have a double orifice. The ninth segment of 

 the abdomen is armed at the tip with four flaps and six hairs, as shown 

 in fig. 4. These flaps are gill-like in appearance, though they are prob- 

 ably simply locomotory in function. With so remarkably developed an 



Fig. Z. — C'dex pungens: Head of larva from below at left; same from above at right— greatly enlarged 



(original). 



apparatus for direct air breathing there is no necessity for gill struct- 

 ures. Kaschke 1 and Hurst 2 consider that the larva breathes both by 

 the anus and by these gill flaps, as well as by the large tracheae which 

 open at the tip of the respiratory tube. Raschke considers that these 

 trachea* are so unnecessarily large that they possess a hydrostatic 

 function. The writer is inclined to believe that the gill flaps may be 

 functional as branchial structures in the young larva, but that they 

 largely lose this office in later life. 



After seven or eight days, at a minimum, as just stated, the larva 

 transforms to pupa. The pupa, as has been repeatedly pointed out 

 with other species, differs most pronouncedly from the larva in the 

 great swelling of the thoracic segments. In this Btage the insect is 



T Raschke, Die Larve von Cults aemorosus, Berlin, l vv 7. 

 2 Hurst, The Pupal stage of Culex, Manchester, 1890. 



