30 THE HOUSE FLY— DISEASE CARRIER 



intestine. The proventriculus is a nodular structure 

 with muscular walls and probably acts also as a pump- 

 ing stomach. The food, passing through the esophagus 

 into the proventriculus, immediately goes by an almost 

 continuous route into the crop. The tube leading into 

 the crop leads out from the proventriculus on the under 

 side backwards and ends in the crop itself, which is a 

 double organ situated in the lower part of the abdomen 

 of the fly. This crop is really a temporary storehouse 

 for the fly's food, and in this storehouse it remains 

 practically unchanged, as has been proved by exact 

 experimentation. Returning from the crop, possibly 

 pumped back by the muscular walls of the proventricu- 

 lus, it recedes again into the true stomach or ventricu- 

 lus, which is a somewhat expanded tubular organ run- 

 ning fore and aft and situated above the tube leading 

 to the crop. The stomach proper extends back through 

 the thorax under the big muscles of the back and into 

 the abdomen, where it ends just over the point where 

 the crop begins to dilate. It runs into the rather nar- 

 row fore intestine, which con volutes upon itself four 

 or five times, and ends in the hind intestine, which in 

 turn ends in the rectum. The intestine is called the 

 hind intestine from the point where the Malpighian or 

 urinary tubules enter. 



Naturally the structure and function of the crop 

 and the proventriculus are matters of considerable in- 

 terest in considering the distribution of disease germs 

 by flies. As Graham-Smith points out, the crop is first 

 distended with liquid food at the beginning of a meal, 



