THE INTERNAL ANATOMY OF THE HOUSE-FLY 5 1 



into a common ejaculatory duct. The external organs consist 

 of a chitinous penis and accessory plates." The male armature 

 is of considerable importance in the classification of certain 

 groups of flies, but need not be considered in detail here. 



The alimentary system commences at the month (Fig. 19, B), 

 which is a cylindrical tube occupying the first half of the proboscis, 

 and passes into the sucking organ ox pharynx (Fig, 19, C), which 

 is supplied with strong muscles and occupies most of the upper 

 third of the proboscis. From the pharynx a thin-walled tube, 

 the cesophagns, runs upwards into the head, through the cephalic 

 ganglion and neck into the thorax (Fig. 19, D). At the junction 

 of the anterior and middle thirds of the thorax it divides. One 

 branch, the crop dnct (Fig. 19, L), is continued backwards into 

 the crop (Fig. 19, J and PI. XV), and the other passes into the 

 proventricnhis (Fig. 19, F), which is situated immediately above 

 the bifurcation. The crop is a bilobed sac, capable of consider- 

 able distension, which when greatly distended loses its bilobed 

 shape, and occupies a large portion of the antero-ventral region 

 of the abdomen. Its walls exhibit unstriped muscle fibres. The 

 proventriculus, into which one branch of the oesophagus passes, 

 is a curious circular organ, flattened dorso-ventrally, and is 

 described by Hewitt (1907, p. 421) in the following way: "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. The interior is almost filled up by a thick circular 

 plug of cells, which have a fibrillar structure, and it is pierced 

 through the centre by the oesophagus. The neck of the plug is 

 surrounded by a collar of elongated cells, external to which the 

 wall of the proventriculus begins, and, enclosing the plug at the 

 sides and above, it merges into the wall of the ventriculus." 

 Beyond the proventriculus the alimentary canal is continued as 

 the ventriculus or chyle stomach (Fig. 19, K), the walls of which 

 are thrown into a number of transverse folds, with saculi between 

 them. The ventriculus passes into the abdomen to become the 

 proximal intestine (Fig. 19, H) which begins at the anterior end of 

 the abdomen and after a number of turns and bends passes into 

 the distal intestine. The junction is marked by the entrance of 

 the ducts of the two malpighian tubes. Each malpighian tube 



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