We pass now to a couple of quite distinct appendages of the digestive canal, namely the salivary glands and the urinary tubules. In fleas the salivary glands are four in number. Two are placed on each side of the anterior end of the flea’s stomach. Each is a simple acinous gland embedded in the body and lined with cells which secrete the saliva. The four ducts from the pairs of glands unite to form two ducts; and 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 just been described, and propels it through the exit duct of the pump into the salivary canal in the mandibles. The pump itself is a hollow chitinous organ. Muscles attached to the walls alternately contract and relax, drawing up the salivary secretion and expelling it through the exit-duct. The opening of the exit-duct is adjusted so as to be opposite to the canals which extend down the mandibles like troughs. It would seem that when the flea is feeding, saliva is pumped into the puncture and blood is pumped out. There is, as it were, an effluent and an affluent stream passing along the mouth parts. The urinary tubules are excretory organs which carry off, in solution, the waste products of the flea’s body. They are sometimes also called Malpighian tubes (Fig. 6). This name they received after Malpighi (1628-94), a famous Italian anatomist, who, four years after Harvey’s death, saw with his own 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. They are longish, slender, tubular glands which are closed at one end, but, at the other, open into the rectum. The urinary excretions come from the blood, pass down the tubes into the rectum, and so leave the flea’s body by the anus. In insects the urinary excretion is, generally, only partially liquid. The organs of respiration in a flea consist of a series of tracheæ, or air-tubes, which open by apertures, called stigmata, at the sides of the body. These air-tubes branch and form an elaborate system of ramifications. They have a horny lining and are supported by a spirally-wound thread-like thickening. In this way air is conveyed from the external world, and the oxygen, which vital processes require, is conducted to all parts of the insect’s body.