PROPHYLAXIS OF MALARIA. 
45 
the Anophelinai , as in this group the palpi are of practically the same 
length as the proboscis and longer than the antenna, while in Culex 
and Stegomyia the palpi in the female are short, club-like structures, 
very much shorter than the proboscis or antenna. As a practical 
working rule it may be stated that any female mosquito having 
palpi approximating the length of the proboscis belongs to the 
Anophelina and, therefore, may be concerned in the transmission of 
malaria. 
The proboscis , or sucking and piercing organ, is a complex structure 
arising from the head between the palpi. It consists of seven parts, 
the labrum, the epipharynx, the hypopharynx, two mandibles or 
lancets, and two maxillae, which, when the insect is not biting, are 
all inclosed in the labium. All of the mouth parts originate beneath 
the clypeus , a chitinous prolongation of the anterior portion of the 
head. At the base of the hypopharynx is situated the so-called 
salivary pump in which the salivary duct empties and is continued 
beyond it into the hypopharynx. The action of this pump is to 
draw the saliva from the salivary glands into the pumping organ 
after which it is forced into the channel along the hypopharynx. 
The saliva is injected into the wound when the mosquito bites and 
with it the malarial sporozoites if the insect is infected. 
The thorax .—The thorax is situated between the head and abdomen 
and is composed of the mesothorax , the scutellum , the prothoracic 
lobes, and the posterior portion, or metathorax. It contains the 
salivary glands and is of importance to entomologists in the classi¬ 
fication of mosquitoes, because of the character of the scales which 
cover it. The legs arise from the thorax, and are six in number, 
and the two icings arise from the upper portion of the thorax and 
their venation is of great importance in classification. 
The abdomen. —The abdomen consists of 10 segments, the posterior 
two being much smaller than the others and containing the sexual 
organs. The scales that cover the abdomen in most species are of 
considerable value in classification to the systematic entomologist, 
as they vary greatly in shape and arrangement. 
The internal anatomy of the Anophelina .—The alimentary canal 
of mosquitoes is divided into a fore-gut , a mid-gut , and a hind-gut. 
The fore-gut lies in the head and thorax and consists of the mouth, 
the pharynx, and pumping organ, the esophagus and the esophageal 
diverticula. The mid-gut begins in the thorax and extends from 
the esophageal diverticula to the hind-gut, filling most of the 
abdominal cavity. It consists of the so-called stomach and the 
pylorus. The portion of the mid-gut known as the “stomach” is 
of special interest to the student of malaria prophylaxis, for it is in 
this portion that the mosquito cycle of the malaria plasmodia begins, 
the ookinete produced by the fertilization of the female plasmodium 
