56 Journal New York Entomological Society. [Vol. xxi. 



general way the larva is able to remain below the surface of the 

 water for a greater or lesser period of time according as these organs 

 are long or short. Thus, for example, the ordinary species of Ctilex 

 (sens, lat.) have them of moderate length and remain beneath the 

 water usually for about a minute; Anopheles, particularly crucians, 

 and some of the less common species of Culex have them shorter and 

 remain for a more brief period beneath the water ; while Culex 

 dupreei and discolor have them greatly developed and are in conse- 

 quence capable of remaining under the water to all appearances indefi- 

 nitely, though both are occasionally seen at the surface. In these 

 latter cases the air-tube has become weak and is probable almost 

 functionless. In Wyeomyia smithii, which remains under water 

 during practically its whole larval life, two of the gills are greatly 

 dilated while two are very much reduced in size. 



There are probably no other insects which spend the whole of their 

 early stages in water that pass through these stages so quickly as do 

 the mosquitoes and in consequence these latter are able to utilize 

 pools which would be quite too transient for other insects. A puddle 

 in a wheel rut can and frequently does bring a brood of mosquitoes to 

 maturity. But despite the fact that only a little water is required 

 for their development, and that when experimentally removed from 

 their place of birth the larvae mature normally and in due season pro- 

 vided the water supplied them has a sufficient quantity of organic 

 matter in it, the species under normal conditions are found in par- 

 ticular environments. 



Our best known species, Culex pipicns, has very appropriately been 

 called the domesticated mosquito by reason of its being invariably 

 found around the habitations of man. Foul water seems to be its 

 natural breeding place. Clear water however quiet and otherwise 

 suitable is never selected. Sewage collected in a gutter, pails con- 

 taining liquid manure, cesspools, rainbarrels, especially when but little 

 water is at the bottom, are favorite breeding places. A small pond 

 may be free from them except where refuse has been thrown in. 

 And it is a noticeable fact that ordinary muddy water or such as be- 

 comes more or less polluted through natural agencies, as through 

 dying vegetation, is not used as a breeding place. Pass beyond the 

 limits of the village and city and Ctdex pipiens is no longer found, 

 its place being taken by an allied species (Culex restuans) more 



