MORPHOLOGY OF MELIBE 537 



(8) The Stomach. 

 a. Pro veil trie u 111 s . 



Following the oesophagus, the alimentary canal enlarges 

 into a chamber 3 mm. long, 1-51 mm. in diameter, and is 

 constricted posteriorly by extensive evaginations of its epithelial 

 lining. This chamber, the glandular stomach or proventriculus, 

 constitutes the preliminary digestive cavity of the alimentary 

 tract. Its epithelial lining is distinctly different from that of the 

 oesophagus, by being highly glandular (PI. 32, fig. 38, Gl). 

 The food is probably kept here until acted on by secretions 

 of the unicellular glands of its columnar epithelial lining. 



h. Gizzard. 



The remaining part of the stomach is the gizzard. Its 

 length in an animal 12 cm. long was 10 mm., with a diameter 

 of 4 mm. at its widest part. The structure of the gizzard is 

 variable. Its walls consist of two coats (PI. 32, figs. 37, 42, 43) 

 or layers, each of which may be divided into two parts. The 

 outer layer consists of a thin outer cover of connective tissue 

 and occasional muscle-fibres, which run longitudinally with the 

 organ (Cc), and of a thick median circular layer (Mus). The 

 inner layer consists of a single layer of tall columnar epitiielial 

 cells of glandular nature (Ept) and a false epithelial cell border 

 (StpT), formed from the secretion of the underlying glandular 

 epithelium. This secretion fuses into a homogeneous mass 

 giving the appearance of a transitional epithelial layer of 

 cornified type (PL 32, fig. 42, Trs, 43, Trp.pl). This cornified 

 border is about as thick (PI. 32. fig. 37) on the dorsal side of the 

 middle part of the gizzard as the other two layers together, 

 and gradually decreases until, on the ventral side. ... it becomes 

 very thin (F). It is far more marked in the anterior part of 

 the gizzard than in the posterior. The glandular nature of 

 the epithelial border is well marked in the anterior part of the 

 gizzard but decreases in the ventral region of this part of the 

 stomach, where the cornified border also entirely disappears. 



