33 



down the gullet into the stomach by successive waves of 

 contraction from before backwards of the muscles actuating 

 the chitinous pharynx (Fig. 14). The stomach is a 



FIG. 14. 



Diagram of the mouth parts of the flea (from Eeport of Com- 

 mission for Investigation of Plague). 1, Muscles operating 

 aspiratory pharynx. 2, Aspiratory pharynx. 3, Mouth. 

 4, Ligament, 5, Epipharynx. 6, Hypopharynx and muscles 

 operating salivary pump. 7, Salivary pump. 8, Salivary 

 duct. 9, Basal element of mandible. 10, Mandible. 

 11, Labium. 12, Basal element of labium. 13, Perioral 

 ring. The thickness of the epipharynx and mandibles and 

 the distance apart of these three instruments is exaggerated. 

 In reality they are apposed and form together the channel 

 through which the blood is sucked. 



FIG. 15. 



Diagram of transverse section of the piercing organ of the 

 flea. Epph, The black part beneath these letters is the 

 epipharynx. M, Mandibles. T, Tube through which 

 blood is sucked. SG, Salivary gland. 



pear-shaped organ occupying a considerable part of the 

 abdomen of the insect. The internal economy of a flea 

 and the arrangements of the mouth-parts may be gleaned 



