iv] INTERNAL ORGANS OF A FLEA 55 



better name, is, however, remarkable. Its function is 

 not quite certainly known. It is a bulbous expansion 

 in the front of the stomach and situated at the junc- 

 tion of the stomach and the gullet. It contains a 

 multitude of chitinous finger-like processes tapering 

 towards their extremities. From their general 

 arrangement the complete collection of processes 

 would act as an effective sort of valve and prevent 

 the return of the fluids from the stomach. It seems 

 most probable that this is their function. During 

 the life of the flea the stomach is constantly churning 

 its contents. Some valvular arrangement between 

 the stomach and the pharynx would seem to be 

 essential; the pharynx is normally collapsed, as the 

 reader may remember, and its walls are drawn apart 

 by muscles attached to its exterior. When the 

 pharynx is full of blood the muscles relax, the walls 

 collapse like elastic, and the blood is forced into the 

 stomach. In many cases a flea will feed when the 

 stomach is already tensely full of blood; and some 

 sort of valve is therefore needed to prevent regurgi- 

 tation into the pharynx when the pharyngeal muscles 

 contract and the walls of the pharynx itself are drawn 

 asunder. 



This valvular arrangement at the anterior end of 

 the flea's stomach has been minutely studied in con- 

 nection with recent plague investigations, because 

 there was a theory that fleas carried infection by 



