13 
impossible thoroughly to search the thickets fringing the village, 
and it may be that these conceal small puddles in which the 
Anopheles breed. 
On August 25th, to our great delight, we discovered a breed- Discovery of 
ing-place of Anopheles in Freetown. This was a muddy puddle f^y^in 8 
by the side of a street (Westmoreland Road) within a few Freetown, 
hundred yards of the foot of Tower Hill. The road here being 
level and running parallel with the line of the hills, the puddle 
was not liable to be scoured out during heavy rain. Its dimensions 
were some 6 feet by 2 feet, and it contained about a score of 
larvae ; a few more were found in smaller road-side puddles 
close by. 
The larvae of Anopheles and Culex, though alike in shape, possess Appearance 
one striking difference in external structure. The respiratory Jarv©^^' 
apertures, Avhich in both cases are placed just in front of the tail, on 
the dorsal side, in the Anopheles larvae open flush with the surface 
of the body ; in the larva of Culex, on the other hand, they are 
placed at the end of a projecting tube (varying in length and 
width according to the species), in which the terminal portion of 
the respiratory ducts is enclosed. The larvae of both genera are 
aquatic, and are obliged constantly to come to the surface of the 
water in order to breathe. But owing to this difference in 
structure, their positions during the act of breathing present a 
striking contrast ; for while Culex larvae hang nearly vertically 
head downwards, suspended by the tip of their breathing tube 
from the surface film, those of Anopheles lie flat on the top of the 
water. The difference in this stage is therefore quite as remark- 
able as is that between the resting attitudes of the perfect 
insects. 
The behaviour of the larvae of the two genera when alarmed is 
also different. Those of Culex at once dart downwards, by 
alternately flexing and extending the body ; Anopheles larvae, on 
the other hand, shoot backwards along the surface of the water, 
w ith a rapid zig-zag motion, lashing their tails side-ways, the first 
stroke apparently being always made to the right ; if much 
frightened, as by an attempt to catch them, they dart to the 
bottom of the puddle like Culex larvae. When at the surface they 
appear fond of lying moored, with their tails in contact with ;i 
patch of green alga, on the margin of the puddle. 
