THE (ESOPHAGUS, STOMACHS AND INTESTINES. 411 



omitted in text-books or treated of as part of the chyle 

 stomach. In the Diptera it is frequently represented by a 

 mere dilatation of its posterior extremity. 



The proximal intestine in Calliphora, and the Muscidae 

 generally, is exceptionally long and forms a flattened helix, 

 which lies on the right side of the middle line ; it is more 

 capacious than the abdominal part of the chyle stomach, makes 

 two turns and a half, then returns on itself and deviates to the 

 left side, where it makes a loop, returns to the middle line, 

 and receives the Malpighian ducts at its posterior extremity. 



Its external surface is smooth, and, except at its upper and 

 its dilated lower extremity, it is lined with conical epithelial 

 cells similar to, but longer than, those of the chyle stomach. 

 Its upper and lower portions, as well as the ducts of the Mal- 

 pighian tubules, are lined with rodded cells like those of the 

 pyloric extremity of the stomach and of the salivary glands. 



The Metenteron (distal intestine or hind gut). I include 

 under this term that part of the intestine which intervenes 

 between the ducts of the Malpighian tubes and the rectal valve. 

 In the Blow-fly the metenteron is very short, its muscular coat 

 is thicker than that of the proximal intestine, and when the 

 intestine is empty it is thrown into longitudinal parallel folds. 

 The epithelium of its upper three fourths is cubical, with a 

 distinct basilar border. The cells are vacuolated and contain 

 numerous granules (PI. XXIV., Fig. 5). 



In the feeding larva, in which the metenteron is very long, 

 its epithelium is loaded with fatty granules, whilst that of the 

 chyle stomach and proximal intestine is clear and transparent. 

 These facts are of interest in relation to the probable function 

 of the Malpighian secretion, and indicate that it is concerned 

 in the digestion and absorption of fat. It will be observed 

 that in the imago, in which fat does not enter into the food, 

 the distal intestine is very short, whilst in the larva it is very 

 long and is always loaded with emulsified fat. 



In the imago the lower part of the distal intestine and the 

 valve which separates it from the rectum are lined by chitinized 

 cells which have spines projecting into the lumen of the gut. 



