iv] INTERNAL ORGANS OF A FLEA 57 



for twelve hours, and at the end of that time were 

 fed on healthy animals. The stomach was then dis- 

 sected out whole and floated in a salt solution. Any 

 adherent organs or muscles were carefully removed. 

 Under these conditions the stomach can be examined 

 and measured under the microscope. The average 

 capacity of a rat-flea's stomach has been approximately 

 estimated to be half a cubic millimetre. 



The stomach of a flea is therefore, comparatively 

 speaking, very large. The blood remains in the 

 stomach in a partially digested condition. It gradu- 

 ally diminishes in volume, showing clearly that 

 absorption is taking place. At the end of so much 

 of the digestive process as takes place in the flea's 

 stomach, the blood has become reduced to a thick, 

 slimy, dark red mass. This passes down the intestine 

 to the rectum, where it is perhaps further influenced 

 by the secretion of the so-called rectal glands. 

 Finally, the undigested remains pass from the rectum 

 in the form of very minute, round, almost black, tarry 

 drops. 



The terminal section of the flea's digestive canal 

 is called the rectum. Here are placed the rectal 

 glands (Fig. 6), which are six in number. Their 

 function seems not to be certainly known. 



The external opening of the rectum is placed at 

 the extreme end of the flea's body between the 

 tergite and sternite of the tenth segment. 



