VIl] 



LIFE-CYCLE 



63 



surface of the water and the larvae hatch out after two or three 

 days. 



In Aides and Psorophora, however, the eggs are laid singly, 

 in most cases not upon the surface of water, but in such situa- 

 tions that the egg lies dormant for some time awaiting favour- 

 able conditions for the development of the larva. In Northern 



OVUM 



Fig. 30. Diagram shewing the corresponding stages in the life-cycle of 

 Anopheles (on the left) and Culex (on the right). From a wall diagram 

 drawn by Professor Nuttall. 



regions it seems that some of the eggs, although they may be 

 repeatedly submerged, will not hatch until they have been 

 frozen, and it is by means of these eggs that the mosquitoes 

 manage to persist through the winter. 



The larva. So far as known the larvae of all mosquitoes are 

 entirely aquatic in habit. The larva possesses a distinct head 



