25 



siphon reaches the surface, fresh air flows into its tracheie, and the phys- 

 ical properties of the so-called surface film of the water assist it in 

 maintaining its position. 



The respiratory tul)e takes its origin from the tip of the eighth ab- 

 dominal 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. 3. These flaps are gill-like in appearance, though they are prob- 

 ably simph^ locomotory in function. With so remarkably developed an 

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

 ures. Easchke^ and Hurst "^ consider that the larva breathes both by 

 the anus and by these gill flaps, as well as b}^ the large tracheie which 

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

 trachete 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 stage the insect is 

 lighter than water. It remains motionless at the surface, and when 

 disturbed does not sink without effort, as does the larva, but is only 

 able to descend by a violent muscular action. It wriggles and swims 

 as actively as does the larva, and soon reaches the bottom of the jar 

 or breeding place. As soon as it ceases to exert itself, however, it 

 floats gradually up to the surface of the water again. The fact, how- 

 ever, that the larva, after it is once below the surface of the water, sinks 

 rather than rises, accounts for the death of man}" individuals. If they 

 become sick or weak, or for any reason are unable to exert sufficient 

 muscular force to wriggle to the surfaces at frequent intervals, they will 

 actually drown, and the writer has seen many of them die in this way. 

 It seems almost like a contradiction in terms to speak of an aquatic 

 insect drowning, but this is a frequent cause of mortality among wrig- 

 glers. This fact also explains the efficacy of the remedial treatment 

 which causes the surface of the water to become covered with a film of 

 oil of any kind. Aside from the actual insecticide effect of the oil, the 

 larva> drown from not being able to I'each the air. The structure of the 

 pupa differs in no material respect from that of corresponding stages 

 of European species, as so admirably figured and described by the older 

 writers, notably Reaumur and Swammerdam^, and needs no description 



^Raschke, Die Larve von Culex nemorosus, Berlin, 1887. 

 ^ Hurst, the Pupal Stage of Culex, Manchester, 1890. 



'Even Bonanni, in 1691, gave very fair figures of the larva and pui^a of a European 

 species. Micrographia Curiosa, Rome, MDCXCI, Pars. II, Tab. I. 



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