28 



Histology of the Gut :i u d G 1 a n d s. 



Tlie digestive tube is lined throughout by columnar 

 epithelium, many of the cells being ciliated, others 

 glandular, aud a cuticle bciug developed in some parts. 

 Beueath the epithelium the wall consists of connective 

 tissue aud elongated muscle fibres. The size of the lumen 

 of the gut varies consideial)ly in dilt'erent parts, as also 

 does the thickness of the walls. The cavity of the gullet 

 is extensive (fig. 15), while its walls are very delicate 

 and closely bound dorsally, by strands of connective 

 tissue, to the outer body wall covering the head. The 

 crop has thick walls and a correspondingly reduced 

 cavity (fig. 22), while the stomach has a very wide cavity 

 with rather thin walls ; the succeeding coil of the gut is 

 narrower aud thin-walled, and the remaining coils are 

 still narrower; the rectum is thicker Availed (fig. 21). 



The sub-lingual pouch, like the rest of the gut, is lined 

 by columnar epithelium, which here has a distinct 

 3'ellow colour, is largely glandular, and probably mucus- 

 secreting. The region of the buccal cavity, into which 

 the buccal glands open, has its walls yellow tinged and 

 somewhat thickened, the thickening being due to the 

 2)resence of the small tubular glands previously 

 mentioned. Their cells resemble those of the buccal 

 glands. The crop has a greater develo})ment of sub- 

 epithelial tissue than is possessed by other parts of the 

 gut, but the major part of the thickening is due to the 

 epithelial folds projecting into its cavity. 



The longitudinal folds are covered by high columnar 

 epithelium, which includes a large number of glandular 

 cells. Many of the cells contain rounded granular 

 highly refractive bodies. Under the epithelium of each 

 fold is a distinct, mainly fibrous, band which can be 



