65 
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 T aeniorhynchus> 
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- 
hynchus , the egg-raft is extraordinarily elongated, 
resembling, in shape, a racing skiff (Fig. 23). 
Culicinae 
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 
by the wind. 
F 
