iv] INTERNAL ORGANS OF A FLEA 53 



muscles and partly by the numerous branching air- 

 tubes through which the insect breathes. Above it 



Fig. 6. Diagram of the alimentary canal of a flea. At the 

 top is shown the orifice of the mouth, leading into the 

 pharynx. Next comes the short gullet. The gizzard is 

 the smaller organ immediately before the stomach. At 

 the base of the stomach are four vermiform tubes, which 

 are the Malpighian tubules. From the base of the 

 stomach issues the intestine, which leads to the rectum, 

 where the six rectal glands are shown. 



lies the heart, and beneath it the nervous cord or 

 chain of ganglia. 



