Colon 



67 



impelled into the space between the wall of the stomach 

 and the peritrophic membrane. The rest of the tube is 

 narrow and uniform. Its wall closely resembles that of 

 the oesophagus, consisting chiefly of annular muscle-cells, 

 each enclosing a number of obscurely striated fibres ; 

 within the muscular coat is a mosaic epithelium. 



The colon, or large intestine, begins as a wide tube Colon, 

 with rather distant bundles of striated, muscular fibres, 

 all annular. In this part of the colon the epithelial 

 cells form transverse rows of large nucleated cells lying 

 between the muscles, and bulging externally (fig. 49). 



m. 



Fig. 48. — Chamber at be- 

 ginning of larval intestine. 

 m, origin of two of tlie Mal- 

 pighian tubules. 



Fig. 49. — Epithelium 

 and annular muscles of 

 larval colon. 



Lower down, the epithelium becomes thinner and less 

 distinct, so that the muscular coat constitutes nearly 

 the whole thickness of the wall. At the same time the 

 diameter of the tube steadily diminishes. There is no 

 rectum, or terminal enlargement, and the colon is con- 

 tinued to the anus, which is situated in the last segment. 



The salivary glands of the larva (fig. 50) form a Salivary 

 pair of thin hollow sacs, situated in the second and 

 third thoracic segments. Each is slightly curved in 



F 2 



glands 



