208 



INSECTS 



and in this respect there is a fundamental difference 

 from those troubles conveyed by house flies, which 

 suffer nothing, and are purely mechanical transporters 

 of the infection albeit peculiarly well adapted for 

 their purpose. 



There are other flies, however, that seem to be nearer 

 the mosquitoes in this respect and, among these, are the 

 species of Glossina or "tsetse" flies of South Africa, 



which are known to pro- 

 duce fatal affections in 

 horses and have been re- 

 cently charged with being 

 agents in the transmission 

 of the "sleeping sickness. " 

 All mosquitoes pass 

 their early or larval stages 

 in water, and that is about 

 the only feature that is 

 common to all of them. 

 They differ widely in the 

 character of the waters 

 which they inhabit, in the 



FIG. pT.-Larva^and^upa of the house per iod of development, and 



in the number of broods. 



Some pass the winter in the egg state, some as larvae 

 and a very fair proportion as adults. All the species 

 that are closely associated with man may breed in 

 dirty water, and some in such as is absolutely filthy. 

 Culeoc pipiens, the common "house mosquito," 

 breeds in rain barrels, lot puddles, cess-pools, gutters 

 and sewer basins. It is rarely found in clean water and 

 almost never in streams or brooks. The eggs are laid 

 in a mass or raft on the surface and are easily seen when 

 their character has once been recognized. In forty- 

 eight hours the larva is ready to hatch, a little lid drops 



