EGGS AND OVIPOSITION. 



The mode of disposal of the eggs shows wide diversities in different genera and 

 epeeies and these affect the entire life-history of the species. The method of 

 oviposition best known is that of the typical species of Culex, and this is shared 

 by Culiseta, Lutzia, Mansonia and U ranoicenia. In these forms the female lays 

 all her eggs at one time, grouping them together in the so-called raft or egg- 

 boat. These eggs are cylindrical, rounded at the ends, and taper slightly 

 towards one end. The eggs are placed in an upright position with the larger 

 end downward and are fastened together along their sides by a viscous secretion 

 which quickly hardens. The slight upward taper of the eggs brings about the 

 characteristic convexity of the bottom of the egg-raft and this prevents it from 

 being overturned. These egg-rafts are deposited either upon the water or close 

 to it. We have found egg-masses of Culex upon the sides of rain-water barrels, 

 some distance above the surface of the water. Egg-masses so placed are probably 

 carried to the water by rain-water, or perhaps even water from a heavy dew, 

 trickling down the walls of the barrel. 



Eeaumur, in his classic work, gives a detailed and most interesting account of 

 the egg-laying process in the common house-mosquito, Culex pipiens. The 

 account of this wonderful observer is so faithful that we reproduce it here : 



" Towards the end of May I left my laboratory work at about 6 o'clock 

 in the morning, to watch the mosquitoes. The thermometer stood at 13-1/3 

 degrees . . . On arriving I first noticed more than thirty egg-masses which had 

 just been laid, but fortunately I saw also a mosquito which had not yet finished 

 oviposition. This mosquito was clinging by her four anterior legs to a bit of 

 leaf touching the side of the bucket. Her body was above the leaf, the penulti- 

 mate segment touching the water. A raft of eggs which was placed near the end 

 of her body and which had not yet reached full size indicated that the laying was 

 well advanced but not yet finished. The mosquito, busy with this important 

 measure, did not notice my presence, and permitted me to approach near enough 

 to her to watch her through a strong lens. I soon knew how it happens that the 

 eggs are placed perpendicularly to the surface of the water and how they are ar- 

 ranged. It is the end of the abdomen which does it all. We have said that the 

 penultimate segment of the body touches the water, and we can now say that the 

 last segment (that which carries the anus) forms with the rest of the body a kind 

 of hook elevated a little above the surface of the water. From this last segment, 

 thus turned up, I soon saw an egg come out ; I saw that it came out in a different 

 direction from that in which the eggs ordinarily issue with other insects. The 

 latter are placed horizontally, or lying down, while these are placed upright, 

 in a vertical direction. The egg issues very near the mass of eggs already put 

 in place. As soon as it is entirely, or almost entirely out, the mosquito has only 

 to push it against those of the little boat which it is nearest to ; for this egg, like 

 those of almost all insects, are without doubt provided with a sticky substance 

 which fastens it to the object to which it is applied. 



" The laying of an egg and the placing it in position is for the mosquito an 

 affair of an instant, and as soon as she has placed one another begins to issue 

 from her body. The mosquito which I observed laid in this way, without inter- 

 140 



