188 MOSQUITOES. 
thus also preventing a direct contact with the water; yet 
this film 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 well-known ‘‘wigglers,’’ so commonly seen 
in rain barrels and watering troughs, This common name 
is well-deserved by the wiggling motion of the larve. 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 larve is greater 
than that of the water in which they move. If they 
move away from this surface film of water, 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 larve feed near the bottom of the water 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 points downward, possesses vibratile organs for 
sweeping minute particles of food into the mouth. In this 
shape the larve have to breathe air, but being surrounded 
by water this would be very difficult if they did not possess 
a cylindrical siphon or breathing-tube at the end of the last 
segment. The tail-like breathing-tube is pushed above the 
water, and the necessary supply of air is thus secured. As 
this does not last very long the larve 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 larve 
which changed in five days to pupz; other larve 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 (4). 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 
