36 THE INTERNAL STRUCTURE OF MUSCA DOMESTICA 



cuius, ventriculus or chyle stomach, proximal and distal intestine 

 and rectum. 



The Pharynx has already been described, and will be further 

 refeired to in the detailed description of the head (pp. 56 et seq.). 

 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 (oes.) 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 pro- 

 ventriculus (Pv.) continuous with, and in the same line as the 

 oesophagus, the duct leading to the crop (fig. 13, 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 {Or.) 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 antero-ventral region 

 of the abdomen. Its walls exhibit muscular (unstriped) fibres; 

 the fiat epithelial cells have a very thin cuticle. The function 

 of the crop will be more fully described later when an account 

 of the method of feeding is given. Graham-Smith has shown 

 (1910) that the capacity of the crop of M. domestica varies 

 between -003 and -002 c.c. 



The Proventricidus (Pv.) is circular and flattened dorso- 

 ventrally. Its structure will be understood by reference to 

 fig. 13. In the middle of the ventral side it opens into the 

 oesophagus, and on the dorsal side the outer wall is continued 

 as the wall of the ventriculus (Ven.). The interior is almost 

 filled up by a thick circular plug (Pv.p.), the cells of which 

 have a fibrillar structure, and is pierced through the centre by 

 the oesophagus. The neck of the plug is surrounded by a ring 

 of elongate cells, external to which the wall of the proventriculus 



