70 FUNCTION OF CROP 



crop-duct, proventriculus and ventriculus. Under these conditions 

 it was seen that the crop contracted and relaxed at frequent 

 but irregular intervals, causing the particles of the pigment to 

 travel backwards and forwards in the crop-duct and its continua- 

 tion, the oesophagus, below the opening of the proventriculus, 

 which remained closed and prevented their passing into the 

 ventriculus. At times the contractions of the crop follow each 

 other in rapid succession. During some of these periods the 

 proventriculus relaxes and allows large quantities of fluid 

 containing particles of pigment to pass into the ventriculus, 

 clearly showing that the proventriculus functions as a valve. 



"Plate XV, fig. I, shows a dissection of the proboscis, 

 oesophagus, crop, proventriculus, and ventriculus of a fly which 

 had been fed on milk and then starved for some time. The 

 crop is nearly empty and the division of the oesophagus is well 

 shown. Plate XV, fig. 2, illustrates a dissection of the same 

 structures in a fly which had been fed just previously with liquid 

 gelatin. The distension of the crop is well shown, though much 

 greater degrees of distension have been often met with. In 

 these photographs the organs have been arranged so as to show 

 the several structures to their best advantage and are not in 

 their natural relation to one another. The complete isolation 

 of the structures as shown on Plate XV is a somewhat difficult 

 dissection, since the oesophagus is very delicate and intimately 

 attached to the chitin in the neck region. It was found, however, 

 that if flies were kept in a cage in a warm incubator (37° C.) 

 they soon gorged themselves on drops of liquid gelatin placed 

 on the floor. On being removed from the incubator after 

 30 — 60 minutes, the whole intestinal canal, including the crop, 

 was distended with gelatin and could be dissected out with ease, 

 especially if coloured gelatin was used in feeding. If it was 

 intended to subsequently cut sections, the flies were fixed with 

 formalin. 



" On several occasions flies which have been allowed to feed 

 on syrup were killed and dissected. The fluid contained in the 

 crop was collected in a capillary pipette and its volume measured. 

 These experiments showed that the capacity of the crop varied 

 between "003 and '002 c.c." 



