56 THE LARVA OF THE BLOW- FLY. 



these cells are firiply cemented together at their base, although 

 they are quite separate towards their apices. The nature and 

 origin of the basement membrane is more apparent in the 

 lingual glands, where it forms the tunica propria. 



The (Esophagus commences at the posterior inferior part of 

 the fulcrum, and extends backward, as a narrow cylindrical 

 tube, to the posterior border of the ninth segment (Fig. lo). 

 Close to its anterior extremity it gives off a diverticulum on its 

 ventral surface, the neck of the crop, or, more properly, of the 

 food sac ; it then passes between the crura of the supra- 

 oesophageal ganglia or hemispheres, lies above the ventral 

 ganglia, and terminates in the proventriculus. 



The length and diameter of the oesophagus and the position 

 of the proventriculus varies with the condition of extension or 

 contraction of the anterior segments of the larva. The figure 

 represents a fully-extended larva ; in the contracted state the 

 proventriculus lies close behind the ganglia. 



The Crop. — The neck of the crop has about the same diameter 

 as the oesophagus. After a short course towards the ventral 

 surface, it curves upwards on the left side towards the back, 

 and dilates into a large sac, which lies over the nerve centres 

 and dorsal vessel. It can be distinctly seen in the living larva 

 through the skin, as it is usually filled with dark gray decom- 

 posing fluid ; when distended, it occupies the dorsal region of 

 three or four segments. 



The epithelial coat of the oesophagus and crop consists of 

 flat cells, and is separated from the lumen by a thick laminated, 

 cuticular layer, which is deeply plicated, processes from the 

 cells extending into the cuticular folds (PI. I., Fig. 2). When 

 the organ is distended, the folds are obliterated, so that the 

 epithelium has clearly an amoeboid character. When these 

 viscera are contracted, the plicated cuticle may fill the whole 

 interior. 



The under surface of the crop has a large group of ganglion 

 cells spread over it — the ' ganglion of the crop.' 



The Proventriculus (PI. I., Figs. 3 and 4) is ovoid, its long 

 axis corresponding with the axis of the body. A longitudinal 



