The Flea

der tube which connects the mouth and the anus, and which is less convoluted and much straighter than in the higher vertebrates. Fig. 6 will show the relative position

position partly by muscles and partly by the numerous branching air-tubes through which the i

ort gullet. The gizzard is the smaller organ immediately before the stomach. At the base of the stomach are four vermiform tubes, which are

ccess to the digestive canal. The first part nearest the mouth is the pharynx which merges gradually into the gullet. Here is placed the pharyngeal pump which is provided with a sucking apparatus. Muscles attached to the dorsal part of the so-called aspiratory pharynx cause it to expand and contract, owing to the elastic reaction of its walls. The o

o add that this organ, neither in appearance nor in use, bears any resemblance to the gizzard

ld act as an effective sort of valve and prevent the return of the fluids from the stomach. It seems most probable that this is their function. During the life of the flea the stomach is constantly churning its contents. Some valvular arrangement between the stomach and the pharynx would seem to be essential; the pharynx is normally collapsed, as the reader may remember, and its walls are drawn apart by muscle

h recent plague investigations, because there was a theory that fleas carried infection by vomiting the septic?

t attached at the hinder end. The gullet having been severed, well in front of the valve, pressure was applied with a blunt tool with the object of forcing the blood through the gullet. The hind aperture of the stomach was, a

During the investigation of the part played by fleas in spreading plague an endeavour was made to measure, as accurately as possible, the average capacity of a rat-flea's stomach when filled with blood. Healthy fleas, taken from Bombay rats, were starved for twelve hours, and at the end of that time were fed on healthy anim

is taking place. At the end of so much of the digestive process as takes place in the flea's stomach, the blood has become reduced to a thick, slimy, dark red mass. This passes down the intestine to the re

e rectum. Here are placed the rectal glands (Fig. 6), which are

at the extreme end of the flea's body between

nd the two ducts thus formed run forward and open into the salivary pump. A spiral chitinous membrane lines the inside of the ducts, keeps them distended, and gives them somewhat the appearance of tracheal tubes. The salivary pump is placed quite in the front part of the insect's head, and is an organ worthy of special notice. It receives the saliva from the glands by means of the two salivary ducts which have

to the puncture and blood is pumped out. There is, as it were, a

eyes the capillary circulation of which Harvey had only inferred the existence. He also was the first to detect the urinary tubes of insects. These tubules answer to the kidneys of the higher vertebrate. They vary in number in different insects from two to over a hundred. In fleas there are four. The

hese air-tubes branch and form an elaborate system of ramifications. They have a horny lining and are supported by a spirally-wound thread-like thicken

ulates in the whole cavity which intervenes between the body-wall and the various internal organs. There is little need for an elaborate system of blood-vessels since the internal tissues are supplied with oxygen by the ramifying air-tubes. Fleas have more of the air-holes called stigmata than any other i

traordinary strength and vital energy of a flea to the fact that, by the blood-system and the air-system, the tissues of the body are kept richly supplied with oxygen. The blood o

ought is too blunt for fine dissections, and it is necessary to sharpen it. This can be done by the help of a rapidly revolving emery wheel, varying the inclination of the needle-point to the wheel, so as to grind off the angles. The flea to be dissected is put in a drop of salt

ector much as we peel off the skin of a shrimp for our tea at the sea-side. The internal organs of the flea then float off in the salt solution; and by using two v

will be found at the side of the stomach with a certain amount of fat round them. Their extractio

he dorsal half of the chitinous carapace. A bold plunge with the right-hand needle will sometimes effect what is desired. A pull on the labium will sometimes bring out the pharynx. It must be confes