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420 0. GORDON HEWITT. 



arise alternately and irregularly from the median abdominal 

 nerve. The median abdominal nerve finally terminates in 

 the genitalia. 



3. The Alimentary System. 



The alimentary canal of the house-fly is shorter than that 

 of the blowfly, and also than that of Glossina described by 

 Minchin (1905), and slightly longer than the alimentary tract 

 of Stomoxys described by Tulloch (1906). It serves as a 

 good example of the Muscid digestive canal. It is of a 

 suctorial character, and consists of pharynx, oesophagus, 

 crop, proventriculus, ventriculus or chyle stomach, proximal 

 and distal intestine and rectum. 



The pharynx has already been described, and will be 

 further referred to in the detailed description of the head. 

 At the proximal end of the fulcrum, where the oesophagus 

 arises, there is usually a small mass of cells, which Kraepelin 

 has described as glandular, but which I believe to be simply 

 fat-cells. 



The oesophagus (figs. 1, 17, 20, ess.) commences at the 

 proximal end of the pharynx, and describes a curve before 

 passing through the oesophageal foramen in the cephalic 

 ganglion, where it narrows slightly. It then passes through 

 the cervical region into the thorax in the anterior region, of 

 which it opens into the proventriculus (figs. 17, 20, Pv,), 

 continuous with, and in the same line as the oesophagus, the 

 duct leading to the crop (fig. 20, d.cr.) passes along the 

 thorax dorsal to the thoracic nerve-centre, and entering 

 the abdomen it leads into the crop, which lies on the ventral 

 side of the abdomen. The oesophagus has a muscular wall, 

 enclosing a layer of flat epithelial cells, and is lined by a 

 cuticular intima, which is thrown into several folds at the 

 anterior end. 



The crop (fig. 17, Cr.) is a large bilobed sac, capable of 

 considerable distension, and, when filled with the liquid food, 

 it loses its bilobed shape, and occupies a large portion of the 



