131 



8. Basal element of rostrum. 



9. Basal element of mandibles. 



10. Salivary pump. 



11. Salivary duct. 



12. Vertical portion, aspiratory canal. 



13. Longitudinal portion, aspiratory canal. 



14. Oesophagus. 



15. Oesophageal ganglia. 



16. Muscles operating aspiratory canal. 



17. Hypopharynx. 



18. Muscles operating salivary pump. 



19. Ligament connecting hypopharynx with floor of aspiratory canal. 



THE ACT OF BITING. 



The epipharynx, or pricker, makes an opening into the skin, through 

 which the mandibles are inserted. These organs, by means of their 

 serrations and independent movement, then enlarge the opening as 

 with a saw, permitting them, with the epipharynx, to pass deeper 

 and deeper until the points of the maxilla rest upon the cutaneous 

 surface. The labial palpi serve as a protective case when the organs 

 are not in action. When in action they serve as a guide to the 

 piercing organs, but are not inserted into the skin. They double up 

 like a bow, on each side, the bend of the bow becoming greater and 

 greater as the biting apparatus passes deeper and deeper. Mitzmain 

 (6) has pointed out that the spring-like action of this bow may assist 

 the flea to withdraw the mandibles and epipharynx. 



During the process of penetration the salivary pump receives saliva 

 from the salivary glands and pumps it down, through the channel 

 in the mandibles, into the wound. It will be seen that the hypo- 

 pharynx, being attached above by a membranous ligament and con- 

 nected intimately with the mandibles below, moves downward with 

 these organs as they pass through the skin. At the same time the 

 muscles attached to its under surface and the salivary pump contract, 

 enlarging the lumen of the pump. When the mandibles are retracted 

 the salivary pump collapses, thereby forcing the saliva out with the 

 movement upward of the mandibles. At the proper time the 

 muscles operating the aspiratory pharynx contract, drawing the 

 canal open and aspirating blood through the canal made by the 

 approximation of the epipharynx and mandibles and into the 

 aspiratory pharynx. When full, the muscles relax from before 

 backward and the pharynx, by means of the elastic reaction of its 

 chitinous lining, contracts and forces the blood backward through the 

 gizzard and into the stomach. It has already been pointed out that 

 the finger-like processes in the gizzard probably act as valves to 

 prevent regurgitation from the stomach. 



