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, 
