158 



BRANCH ARTHROPODA 



short palpi, while the Anoph'eles has palpi nearly as long as the beak, making 

 three long projections on the head. It may be distinguished also by the 

 way it alights. The Culex is " hump-backed " with the beak pointing down- 

 ward, while in the Anopheles the body and beak lie in the same plane. The 

 eggs of Culex are laid in a boat -shaped mass, while the eggs of Anopheles 

 are laid " singly and at random," but run together, forming irregular groups 

 or strings. The larva of Culex hangs with the head down, so as to keep the 

 end of the respiratory tube, which is borne by the next to the last somite, in 

 contact with the air. The larval stage lasts about five or six days or longer 

 in unfavorable conditions. The larva of Anopheles has a very short respi- 



Fig. 130. A fine breeding-place for mosquitoes. (Hampton Leaflet.) 



ratory tube, and consequently lies in a horizontal position just under the 

 surface film in order to obtain air. (This explains how it is that kerosene 

 oil " poured upon the troubled waters " destroys the larvae. They are 

 simply drowned or suffocated as the surface film of oil excludes the air.) 

 The larval stage lasts from twelve to fourteen days. 



The mosquito larva, after growing several days and molting twice, changes 

 into a club-shaped pupa (Fig. 126), the head and thorax being greatly en- 

 larged, while the abdomen is slender. At the caudal end is a pair of leaf- 

 like locomotor or swimming appendages. It takes no food, and when un- 

 disturbed it floats upon the water, but when disturbed it is active, thus differ- 



