function of crop /i 



Feeding Experiments. 



Fluids. — Plain and coloured syrups. 



" A series of feeding experiments with plain and coloured 

 syrups was conducted in the following manner. Flies which 

 had been kept for 24 hours or more without food were placed in 

 clean cages and a few drops of syrup, made by dissolving brown 

 sugar in water, placed on the glass floor plates. The flies began 

 to feed almost immediately. It was noticed that the flies 

 approached the drops and inserted their proboscides, but in 

 many cases did not touch the drops with their legs. Occasionally 

 the anterior legs were placed on the drops, but even then in 

 many instances they did not appear to be soiled. If the drops 

 were too close together, or were irregular, then the feet often 

 became soiled. Occasionally a fly would fall into a drop and 

 subsequently drag itself about the plate spreading the syrup and 

 causing other flies which walked over the wet areas to soil their 

 feet. 



" If undisturbed a fly usually becomes gorged within a minute 

 or less. Previous to feeding, the ventral surface of the abdomen 

 of a hungry fly when viewed from the side is slightly concave. 

 Immediately after feeding, the anterior half of the abdomen is 

 greatly distended while the posterior half may still remain 

 concave. This is due to the fact that the greater part of the 

 food is first taken into the crop, which occupies the anterior 

 portion of the abdomen, and greatly distends that organ. 

 Plate XVI, fig. I, represents the side view of an average unfed 

 fly (x 7) and Plate XVI, fig. 2, the side view of a fly immediately 

 after feeding on syrup. In the latter case the distention of the 

 crop, which can be plainly seen, was so great that the lower 

 portions of the tergal abdominal plates, which usually overlap 

 each other, were forced some distance apart. Experiments with 

 syrup coloured deep red with carmine or deep blue with nigrosin 

 show very clearly the passage of the food material into the crop. 

 As the fly feeds on carmine syrup a red area appears on the 

 anterior portion of the ventral surface of the abdomen, and 

 gradually enlarges till it occupies the whole of the anterior 



