72 FUNCTION OF CROP 



two-thirds of the surface of the abdomen, and usually shows a 

 more or less well-defined convex posterior margin. (PI. XVI, 



fig- 3-) 



" On rare occasions the red area is situated near the posterior 

 end of the abdomen, but is continued forwards to the thorax as 

 a distinct median red line between colourless areas. In such 

 cases dissection shows that the crop has been displaced by the 

 distension of the large abdominal air sacs. 



" Sometimes the flies continue to feed after the crop is full, 

 and then the food passes directly into the intestine, and after a 

 time the whole ventral surface becomes coloured. 



" In order to check these observations a number of flies 

 were killed and dissected (under a Zeiss binocular dissecting 

 microscope) at various times after feeding on carmine syrup. 

 The dissections showed that the crop was almost invariably 

 distended with coloured material before any was found in the 

 intestine. If feeding had continued beyond this point coloured 

 material was found in the upper part of the intestine, and within 

 a short time in the lower portion also. In one series of 

 experiments, for example, hungry flies were fed on carmine 

 .syrup and killed and dissected at short intervals. 



TABLE 3. S/iozvitig the rate at wJiicJi food passes fi-oin the 

 crop into the in test vie. 



rj,- f. r 1- No. of flies T) ,.,,u 



lime after feedmc; j- . a Result 



^ dissected 



3 minutes ... ... 1 Crop full of red fluid, but none found in 



ventriculus or intestine. 

 6 ,, ... ... I Crop full of red fluid, but none found in 



ventriculus or intestine. 



10 ,, I Crop full of red fluid, and some just be- 



ginninsT to pass into the ventriculus. 

 15 ,, ... ... I Crop fuii of red fluid, and upper third of 



intestine red. 

 20 ,, ... ... I Crop full of red fluid, and upper third of 



intestine red. 

 T, Crop full of red fluid, and upper third of 



intestine red. 



, ' 4 Crop full of red fluid, and upper half of 



^ '^o"'-^ - ' intestine red. 



I I Crop full of red fluid, and up[)er three- 



^ quarters of intestine red. 



