50 
A Monograph of Culicidae. 
cannibal’s own destruction. The position in the water is much 
like Coreihra ; they seldom come to the surface, but do now and 
then, and place their respiratory tube above the surface film 
and remain for a long time almost motionless. It often occurs 
in large troops, and is sometimes found with Gulex. 
It will thus be seen that there is some variation in habits, by 
noticing which we may tell anyhow Culex, Anopheles , and Coreihra 
at once from one another, and that there is also variation in 
the habits of the different species in the genus Culex itself. 
THE EFFECT OF RUNNING WATER ON THE LARVAE. 
Although we mostly find Anopheles and Culex larvae in still 
water, they can nevertheless live in running water, I have 
found both in the Cam, when the water was running at the rate 
of about half a mile an hour. Celli has made a number of 
measurements with regard to the velocity of water ensuring 
against the development of Anopheles larvae. It is stated that 
water must flow not under 1900 yards per hour to prevent their 
development. 
Where water flows at and above this rate we may be sure 
neither Anopheles nor Culex can live. Can this knowledge be 
made of any practical use ? Sir William MacGregor apparently 
thinks so, for he has said, regarding Lagos,* “ One thing could be 
done ; Lagos Island could be surrounded by a sea-wall that would 
render the current there generally too fast for the Anopheles.’' 
By such means no doubt one great source of generation of these 
pests might be obliterated, but as they breed in countless other 
places, would it be worth the enormous cost ? Would not it be 
simpler to treat the affected human inhabitants ? 
PUPAE OF CULICIDAE. 
The pupae in the Culicidae, unlike the typical dipterous pupa, 
are active creatures, rising and falling in the water at will, but 
not to the same extent as do the larvae; they do not fall so 
easily, but descend by violent muscular contractions of the tail; 
they swim with ease, and reach the bottom of the butt or tank 
* Journal Trojucal Medicine, no. 27, vol. iii. p. 67. 
