166 BIOLOGY. [Boox n. 



ruminants : the paunch, the bonnet, the manyplies and the 

 caillette, this last division being more specially charged with the 

 secretion of the gastric juice (Fig. 11). 



The stomach of the vertebrates debouches into the intestine 

 properly so called, or rather into the first part of that intestine, 

 the duodenum, and has continuation in the small intestine. It 

 is however distinctly separated from it by a membranous fold 

 called the valvula of the pylorus. 



In its region nearest to the stomach the intestine receives the 

 excretory conduits of two of the most important glands, the 

 liver and the pancreas. The median or small intestine is, with 

 some exceptions, longer in the herbivorous than in the carnivorous 

 vertebrates. There are exceptions to this rule, but they are 

 more apparent than real ; for, in effect, the development ini 

 width usually comes to compensate for the defect in length. The 

 mole, the cetaceans, though carnivorous, have very long, but at 

 the same time very narrow intestines. 



Caterpillars have an intestinal tube, which is not much longer 

 than their body, but it is nearly as wide. 



The last portion of the digestive tube, the large intestine, really 

 develops itself in length and breadth only in the amphibia. 

 Beginning with reptiles, the large intestine is furnished on its 

 passage with a dilatation called caecum, much more developed in 

 herbivorous than in carnivorous animals. 



In the termination of the intestine we likewise remark an 

 unequal differentiation in the diverse vertebrated groups. In the 

 selacians, the amphibians, the reptiles, the birds, and the mono- 

 trematous mammifers, the large intestine opens into a cavity 

 called cloaca, into which debouch the urinary conduits, and the 

 genital conduits. 



We have not here to give a detailed description of the 

 structure of the digestive tube, and we content ourselves with 

 recalling that, in the vertebrates, its walls are composed funda- 

 mentally of three tunics encased in each other, and intimately 

 connected. They are, from within to without, a mucous 



