188 MOSQUITOES. 



thus also preventing a direct contact with the water; yet 

 this fihn disappears from the exposed surface of the eggs by 

 evaporation as soon as the raft is in a proper position. In 

 three to five days these eggs hatch and produce from the 

 lower ends the w^ell-kno\\''n "wigglers," so commonly seen 

 in rain barrels and watering troughs. This common name 

 is well-deserved by the w^iggling motion of the larvcC. These 

 feed mainly below the surface of the water, and move just 

 below it, as if it were a solid substance. This is a very 

 queer thing, as the specific weight of these larvae is greater 

 than that of the w^ater in which they move. If they 

 move away from this surface film of w^ater, they invariably 

 sink to the bottom, at least they do if not using their swim- 

 ming plates at the ends of their tails. The larger and 

 stronger larvcE feed near the bottom of the w^ater upon de- 

 caying vegetable matter, and only rise to the surface to ob- 

 tain air. Such a larva (a) has a large head and thorax, 

 while its abdomen is much more slender. Its head, which 

 usually j)oints downward, possesses vibratile organs for 

 sweeping minute particles of food into the mouth. In this 

 shape the larvae have to breathe air, but being surrounded 

 by water this would be very difficult if they did not possess 

 a cjdindrical siphon or breathing-tube at the end of the last 

 segment. The tail-like breathing-tube is pushed above the 

 water, and the necessary supph^ of air is thus secured. As 

 this does not last very long the larvae are forced to repeat 

 this operation quite frequently. The larval stage lasts but 

 a very short time in some species of mosquitoes, while in 

 others it extends over a much longer period. This depends 

 to some extent upon the season. The writer kept larvae 

 w^hich changed in five days to pup£e; other larvfe of a differ- 

 ent species of mosquito require almost three weeks to reach 

 their full size. During this period the latter ones moulted 

 three times. When full grown a very remarkable change 

 takes place, and a club-shaped pupa with greatly enlarged 

 head and thorax, is now- seen (h). The strange part of this 

 wonderful change is the possession of two slender breathing- 

 tubes upon the back of the thorax instead of a single one in 

 front of the tail. Though the pupa does not require any 



