246 BACOT : MOSQUITOES AND THE DANGER OF MALARIA.
so that the perfect mosquito emerges into the air from the pupa-
case, which serves as a raft to support it during the process of
ecdysis.
So far as exact knowledge extends, female mosquitoes require
a meal or meals of blood before they can develop their ovaries.
In a few cases, out of a large number of experiments, eggs have
been laid by females fed on syrup and other foods ; but the
number of successes compared with the number of failures
suggests that the former are exceptions which tend to confirm
the rule. It has been suggested, because mosquitoes are known
to swarm in Arctic wastes where they can hope to obtain blood
at rare intervals only, that they must be able to produce eggs
on some diet other than blood ; but the argument is not conclu-
sive. The facts are capable of explanation on other assump-
tions—as, for instance, that some of the eggs of each batch
laid may remain dormant for long periods before hatching.
Male mosquitoes do not suck blood. The few recorded
exceptions of this rule are thought by Edwards to be due, possibly,
to the action of females with male secondary sexual characters.
The males are known to feed on syrup ; also to visit flowers
and decaying organic matter. Further, they will at times
insert their proboscis into the skin pores, probably to suck up
perspiration.
The blood required by the females need not necessarily
be human. It is probable that a few only of the many species
habitually attack man (Edwards estimates that there are
upwards of 1,000 species, only 18 of which occur in Britain).
What seems certain, however, is that the species which do
suck man's blood exist in innumerable, numbers ; so that possibly
it would be correct to state that the greater proportion of these
two-winged fiends are inimical to man. It is probable, however,
that man is not really the normal host of a large number of
species which habitually attack him when opportunity occurs ;
and it is, at the same time, certainly true that many of the
species closely associated with man will feed on the blood of
other animals when pressed for food.
Mosquitoes are very prolific insects. Some Anopheles
mosquitoes are stated to lay as many as 1,500 eggs. I have
known the species associated with yellow fever to lav upwards
of 1,000. The raft-making species are stated to lay from 120