58 THE FLEA [CH. 



We pass now to a couple of quite distinct 

 appendages of the digestive canal, namely the sali- 

 vary 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. 



