THE ALIMENTARY CAXAL AXD ITS APPENDAGES. 



125 



sharp longitudinal corrugations. Between the six epithelial bands 

 and the muscular layer are as. many triangular spaces, in which 

 ramify tracheal tubes and fine nerves for the supply of the 

 epithelium. The chitinous layer is finely setose. The muscular 

 layer consists of annular fibres strengthened externally by 

 longitudinal fibres along the interspaces between the six 

 primary folds.* 



Fig. 69. Transverse section of Small Intestine and Colon, close to their 



junction. X 50. 



The corrugated and non-epitheliated interspaces may be . 

 supposed to favour distension of the rectal chamber, while the 

 great size of the cells of the bands of epithelium is perhaps due 

 to their limited extent. Leydigf attributed to thes.e rectal 

 bands a respiratory function, and compared them to the 

 epithelial folds of the rectum of Libellulid larvae, which, as is 

 well known, respire by admitting fresh supplies of water into 

 this cavity. It is an obvious objection that Cockroaches and 

 other Insects in which the rectal bands are well developed do 

 not take water into the intestine at all. Gegenbaur has there- 



; " The epithelial bands of the rectum of Insects were first discovered l>y 

 Swammerdam in the Bee (Bibl. Xat., p. 455, pi. xviii., fig. 1). Duf our called them 

 muscular bands (Rech. sur les Orthopteres, &c., p. 369, fig. 44). 



t "Lehrbuch der Histologie," p. 337. 



