ORDER DIPTERA : THE NEMATOCERA, ETC. 51 



spawn {Corethrd), or in groups or "rafts" (e.g. Culex), or 

 singly (e.g. Anopheles). The individual egg is oval, with one 

 end blunter than the other, and has a pigmented chitinous 

 shell. A very fine external membrane either adheres closely 

 to the shell, or invests it more or less loosely (as in Anopheles) 

 so as to leave a space or " float " on either side of the egg. 

 The eggs of some species may hatch within twenty-four 



breathing tube 



Iracheal thinks 



Fig. 12. — Larva of S(ejomi/io/osda!a. 



Fia. 13.— Larva of an A^.n\ 



hours in the hot season in the tropics, but cold retards their 

 development. 



The larvae (Figs. I2, 13) show considerable differences of 

 structure and habit, and the following general description, 

 which, however, does not apply to Corethra and Mochlonyx, 

 is meant to clear the way for subsequent consideration of the 

 specific forms. They are specially formed for an aquatic 

 life and are unable to live out of water, and they may be 

 found in collections of water of any kind, small or large. 



