CHAPTER XI 

 NUTRITION IN ANIMALS 



The living body is the theatre of many chemical and physical 

 operations in line with those of the inorganic domain. 



Thomson. 



WE have now considered the form and supporting struc- 

 tures of the body wall of a typical Vertebrate; in other 

 words, the outer tube which surrounds and contains the 

 viscera. Through this outer tube, just as in the case of the 

 Earthworm and Crayfish, there runs from mouth to anus a 

 second or inner tube, the alimentary canal, which has been 

 mentioned incidentally in describing the various regions of 

 the Vertebrate body. 



A. THE ALIMENTARY CANAL 



The entrance to the alimentary canal is the mouth, a trans- 

 verse ventral aperture near the anterior end of the head, 

 which leads into the BUCCAL CAVITY supported by the jaws. 

 The buccal cavity merges into the PHARYNX, or throat, which 

 in turn leads by a narrow passage, the OESOPHAGUS, to the 

 STOMACH. (Figs. 74, 82-88.) 



In the aquatic Vertebrates the region of the alimentary 

 canal from the mouth to the oesophagus acts as a common 

 food and respiratory passage. The food passes on through the 

 oesophagus to the stomach, while the water makes its exit by 

 a series of perforations, or gill slits, through the pharynx and 

 body wall directly to the exterior. During this passage the 

 respiratory interchange of gases takes place. Among the 



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