a handbook of the mosquitoes of north america - Systematic Catalog ...

RELATION TO WELFARE 49
at the end of about forty-eight hours. The escape o.f so many
merozoites with their wastes corresponds with the onset of a
chill followed by a marked rise in the temperature of the pa-
tient. Hence this type is known as the tertian or three day
fever, the chill and fever appearing on the third day. After
the asexual cycle has continued for a number of days, there
appears a new stage in the cycle of the parasite. This is known
as the sexual stage. Certain merozoites now develop into
male and female gametocytes or sex cells (Fig. 16, Nos. 8,9 and
10). Two kinds are produced male, wzicvogawzetocytes, and
female, nfzacroga,we tocy tes. These now remain in the blood
cells and no further development takes place in man.
At this point the anopheline mo,squito becomes essential to
the continuance of the life of the parasite. If a person con-
taining the micro- and macrogametocytes in his blood is bitten
by an anopheline (as A. quadrinzaculatus) mosquito and num-
bers of these sex cells are obtained, a further remarkable de-
velopment takes place in the stomach of the mosquito. The
female or macrogametocyte matures into what is called a
macrogamete and is now ready for fertilization. The male
or microgametocyte gives off a number of small linear bodies
which are the true nzicroganutes or male elements (Fig. 16,
No. 11). These lash about till they find a macrogamete and
one of them immediately penetrates it (Fig. 16, No. 12) and
completes the process of fertilization. The union of the male
and female cells produces a zygote (No. 13). The zygotes
are produced in the stomach of the mosquito. The zygote,
at first passive, soon elongates and begins active movement,
hence the name ookinvzete (No. 14). The ookinete penetrates
the wall of the stomach and establishes itself between the
epithelial layer and the muscular layers (No. 15). Here it
becomes spherical and grows very large by the absorption of
food from the surrounding cells, and is called an oocyst (No.
16). Within the oocyst, remarkable changes (sporogony)
take place and at the end of four or five days, the oocyst is
completely filled by very minute organisms-the sporozoites