Chapter VII 

 THE OVUM 



Ova are minute bodies one mm. or less in length. 

 When first laid they are white in colour but rapidly 

 become brown or black. They occur on the surface 

 of water, and if submerged do not hatch out. Mosquito 

 eggs may be laid by the edge of water, or on floating 

 objects, or upon the water. In the last case, they have 

 some device to ensure that they shall float, and not 

 sink and be destroyed. In the case of Anophelines and 

 some species of Stegomyia (Fig. 22), each ovum lies 

 separately upon the water, and has air cells which keep 

 it afloat. In the case- of Culex and Taeniorhynchus, 

 hundreds of eggs are cemented together to form rafts, 

 each egg lying perpendicularly, with its larger end 

 pointing downwards. In Culex, the egg-rafts are 

 broad and roughly oval in shape (Fig. 21). In Taenior- 

 ky nchus , the egg-raft is extraordinarily elongated, 

 resembling, in shape, a racing skiff (Fig. 23). 



CUL 



ICINAE 



Culex. Examine the surface of some semi-putrid 

 water for egg-rafts of Culex. Egg-rafts can almost 

 always be found on the surface of water containing 

 macerating leaves, fruit, etc. They are bodies of 

 a blackish-brown colour, and are readily wafted about 

 bv the wind. 



