48 
PROPHYLAXIS OP MALARIA. 
water, but owing to the absence of the respiratory tube in the Ano- 
phelince the larvae always lie horizontal to the surface. This fact 
makes the differentiation of these larvae very easy, but, as Ludlow 13 
has pointed out, other aquatic larvae have this peculiarity, so that 
one must be familiar with mosquito larvae before concluding that 
anophelines are present. 
The larvae vary in color, but are usually gray or brownish. They 
molt four times before becoming pupae, and the length of this stage 
of development varies greatly, the average probably being from 10 
to 14 days, although it has been observed to be as*short as a week 
and as long as 30 days. It varies with different species and with 
external conditions. 
The pupce. —The pupal stage of development is probably the 
shortest, averaging about two days, but varying between two and 
six days according to temperature and other external conditions. 
The pupae are not easily differentiated from those of other mosqui¬ 
toes, and, therefore, will not be described. 
The adult mosquito or imago. —After a period of development 
varying in time, but usually in from two to four days, the pupa 
rises to the surface of the water, remains there, and the skin over 
the thorax breaks open and liberates the adult insect. This process 
has been very accurately described by Hurst 14 , to whose work the 
reader is referred. 
Habits of mosquitoes of importance in the prophylaxis of mala¬ 
ria. —A knowledge of the habits of the larvae and the adult anoplieline 
is of importance in the prophylaxis of malaria, for the better ac¬ 
quainted one is with this portion of our subject the easier will be the 
application of methods looking to the destruction of these insects. 
Habits of the larvae. —I have already spoken of the position of the 
larvae of anophelines being parallel with the surface of the water, 
and this position is maintained unless the larva is frightened, when 
it will sink below the surface. It feeds upon floating objects, which 
are attracted to the mouth by the fringes of the mouth parts pro¬ 
ducing a current toward the mouth. The larvae eat both vegetable 
and animal matter and devour one another. 
The larvae of some species of Anopheles are able to hibernate , as 
shown by the observations of Galli-Valerio and de Jongh. They 
found that the larvae of Anopheles bifurcatus hibernate beneath the 
leaves of aquatic plants, and that they survived even when in water 
between two sheets of ice. 
Of the natural enemies of mosquito larvae may be mentioned the 
fresh-water hydras, many aquatic insects, salamanders, and certain 
species of fish, to be hereafter considered. 
Habits of the adult anopheles — Feeding. —The feeding habits of 
the species of anophelines that frequent the habitations of man are 
