FUNCTION OF CROP 69 



the fluid is drawn up through the proboscis into the pharynx by 

 the action of the dilator muscles of the pharynx and, as will be 

 shown presently, the crop is first distended with liquid food. 

 If the feeding is continued after the crop is fully distended, the 

 food may pass directly into the ventriculus through the pro- 

 ventriculus. If, on the other hand, the fly is disturbed before 

 any portion of the food has entered the intestine, the fluid which 

 has been sucked into the crop is gradually passed into the 

 ventriculus. In any case, after a variable period of time, the 

 contents of the crop pass into the intestine. The proventriculus 

 is capable, therefore, of being closed during the early part of a 

 meal in order that the food may not enter the intestine but pass 

 into the crop. On the complete distension of the crop, it opens 

 in order to allow food to pass directly from the proboscis to the 

 intestine. It also opens when it is necessary to allow material 

 to pass from the crop into the intestine. After a meal flies 

 usually regurgitate some of the fluid contents of their crops 

 through the proboscis, and during this process the lumen of the 

 proventriculus is closed in order to prevent the fluid from passing 

 into the intestine. Lowne (p. 409) regards the proventriculus 

 as a 'gizzard and nothing more,' and Gordon Hewitt (1907, 

 p. 421) states that 'its structure suggests a pumping function 

 and also that of a valve,' while Giles (1906) says that 'taking 

 the structure as a whole, it is difficult to resist the idea that it 

 must, in some way, have a valvular function, though it is difficult 

 to say how.' The observations just quoted, of which some 

 particulars are given later, seem to indicate that it acts as a 

 valve, possibly controlled, at will, by the fly" (Graham-Smith, 

 1910, p. 4). 



Since the paper quoted above was published, the writer has 

 carried out a number of experiments on blow-flies to determine 

 the function of the proventriculus by direct observation. Blow- 

 flies were allowed to feed on syrup containing particles of Indian 

 ink and immediately afterwards anaesthetized with chloroform. 

 The insect was then fastened down on its side by means of 

 hot sealing-wax at the bottom of a shallow tray, which was 

 immediately filled with water. As rapidly as possible the upper 

 side was dissected away so as to expose the thoracic oesophagus. 



