46 
PROPHYLAXIS OF MALARIA. 
bv the male penetrating the wall of this portion of the intestinal 
canal and forming the cyst in which are produced the sporozoites. 
This portion of the mid-gut lies at about the level of the sixth ab¬ 
dominal segment. 
The hind-gut begins at the pyloric dilatation into which open the 
five Malpighian tubes and ends at the anus. It consists of the 
pyloric dilatation, the ileum, the colon, and the rectum. 
The genital organs , while of great importance to the entomologist 
in the classification of species, will not be described, as they can not 
be used for this purpose by the ordinary observer. 
The salivary glands .—The salivary glands are situated in the ante¬ 
rior portion of the thorax and are of interest because it is through 
them that the malaria sporozoites reach the mosquito’s proboscis 
and eventually the blood of man, being injected into the wound when 
the insect bites. The glands are two in number, each consisting of 
acini lined with large granular cells and possessing a central duct 
which unite, after leaving the acini, to form a common salivary duct 
which enters the alimentary canal close to the base of the proboscis. 
It is in the cells lining the tubular salivary glands that the malaria 
sporozoites are found at the termination of the cycle of development 
of these parasites in the mosquito. 
The life-cycle of the Anophelince .—The Anophelince , in common 
with all mosquitoes, passes through larval and pupal stages before 
development into the perfect insect and these stages are aquatic so 
far as we know. 
The ova .—The ova of Anopheles are generally laid upon the sur¬ 
face of water but a few species will lav them in wet ground, as I 
have observed in the Philippines. The eggs are not laid in boat¬ 
shaped masses, as in the case of the common Culex mosquitoes, but 
singly, and by adhering end to end geometrical patterns are some¬ 
times produced that are quite characteristic. The distinguishing mark 
of the eggs of the Anophelince is the presence of the so-called “ float,” 
a hydrostatic organ composed of a partial envelope expanded along the 
middle of the egg. giving it a very characteristic appearance. These 
lateral floats are, variously marked in the eggs of different species and 
vary in size but are always easily distinguished and of the greatest 
service in differentiating the anopheline egg from that of other mos¬ 
quitoes. The eggs are oval in shape and eggs hatch, in most species, 
in from one to two days, but this varies so much with external condi¬ 
tions and with the different species that a general statement is hardly 
justified. From thirty to over a hundred eggs may be deposited by a 
single female. 
The eggs will remain alive in moist mud for considerable periods 
of time, even as long as 6 days, but can not resist complete drying for 
over 12 hours, so far as is known. This fact is important, as it indi- 
