BACOT : MOSQUITOES AND THE DANGER OF MALARIA.
247
to 400 in a raft, but these figures probably do not represent the
full count, as the female probably lays more than one raft of
eggs during her life.
The female mosquito's sucking apparatus (fig. 1, Pl. iv.)
consists of the labrum and epipharynx, which form a gutter,.
with a narrow opening along its ventral side (Pl. iv.—8 and 9).
This slit is covered in by the slender hypopharynx, thus com-
pleting the tube through which the blood is pumped into the
gullet. The mandibles and maxillae, armed at their tips with
delicate saw-like teeth (Pl. iv.—3. 4, and 6), serve to cut a
deep slit-like hole through the skin, down which the feeding
tube is thrust, or more probably lowered.
The blood, after passing up the sucking-tube, passes through
the pharyngeal pump and thence through the oesophagus into
the stomach. Just before the junction of the oesophagus with
the stomach are three bag-like diverticula, two small ones
situated dorsally and a much larger one ventrally. These
probably correspond with the food-reservoir or sucking-stomach
of the house-fly, etc. The use of these thin-walled chitinous
sacs in the mosquitoes is thought to be chiefly as air chambers,
probably associated with the adjustment of the specific gravity
of the insect during flight. Authorities differ as to the purpose
of the large ventral one. Some incline to the view that it is used
as a food-reservoir, and state that, after a meal, fruit juices
or blood may be found in it. When dissecting gorged females
of Stegomyia fasciata, I never found any blood in it. The
salivary glands, which play such an important part in the trans-
ference of the malarial germs to man, are relatively-large three-
lobed organs. The ducts which issue from them join and dis-
charge through a common duct into a minute tube which passes
down the thickened central portion of the hypopharynx (Pl.
iv.—8 and 9).
While the exact purpose and nature of the salivary secre-
tions of blood-sucking insects are still questions for discussion,
it has been shown by Nuttall and Shipley for the mosquito, and
by Nuttall for the louse (Pediculus humanus), that they have a
retarding influence as regards the coagulation of the blood.
These facts do not, however, necessarily exclude other opinions.
Some incline to the view that the saliva reduces the capillary
resistance to the flow of blood up the proboscis : others hold
that the fluid mingles with the blood and aids its digestion. A