THE ALIMENTARY CANAL AXD ITS APPENDAGES. 



117 



In the oesophagus they are very long, and grouped in bundles 

 along sinuous transverse lines. In the crop the hairs become 

 shorter, and the sinuous lines run into a polygonal network. 

 The points of the hairs are directed backwards, and they no 

 doubt, serve to guide the flow of saliva towards the crop. 



The gizzard has externally the form of a blunt cone, attached 







by its base to the hinder end of the crop, and produced at the 

 other end into a narrow tube (J to J in. long), which projects 

 into the chylific stomach. Its muscular wall is thick, and 

 consists of ruanv layers of annular fibres, while the internal 



/ / 



cavity is nearly closed by radiating folds of the chitinous lining. 

 Six of the principal folds, the so-called " teeth," are much 

 stronger than the rest, and project so far inwards that they 

 nearly meet. They vary in form, but are generally triangular 

 in cross section and irregularly quadrilateral in side view. 



Fig. 59. Transverse section of Gizzard of Cockroach. The chitinous folds are 

 represented here as symmetrical. See next figure. X 30. 



Between each pair are three much less prominent folds, and 

 between these again are slight risings of the chitinous lining. 

 A ridge runs along each side of the base of each principal tooth, 

 and the minor folds, as well as part of the principal teeth, are 

 covered with fine hairs. The central one of each set of 

 secondary folds is produced behind into a spoon-shaped process, 

 which extends considerably beyond the rest, and gradually 

 subsides till it hardly projects from the internal surface of the 

 gizzard. Behind each large tooth (i.e., towards the chvlific 



C_7 CJ \ / 



