68 MANUAL OF ZOOLOGY sect. 



consists either of cartilage, or of bone, or of both. The 

 parts of the skeleton in the higher animals, whether external 

 or internal, usually consist of a number of distinct pieces 

 which are movably articulated together, and these have the 

 additional important function of serving for the attachment 

 of muscles, constituting a jointed framework on which the 

 muscles act in bringing about the various movements of the 

 body and its appendages (Fig. 30). 



The nutrition of the Metazoa is in some cases, as in some 

 of the Protozoa, effected by food being absorbed in a 

 dissolved form through the general surface. In the great 

 majority, however, the food, liquid or solid, is received 

 through an opening — the mouth — into a cavity in the 

 interior of the body — the digestive or enteric cavity. In 

 most cases this has the form of a longer or shorter tube or 

 canal, beginning at the mouth and ending at a second exter- 

 nal opening — the anus. This digestive or enteric canal 

 consists usually of a number of different parts, through which 

 the food passes in succession, each part having its special 

 function to perform in connection with nutrition. In most 

 cases there are organs in the neighbourhood of the mouth 

 serving for the seizure of food ; these may be simply tentacles, 

 or soft, finger-like appendages, or they may have the form of 

 jaws, by means of which the food is not only seized but torn 

 to pieces, or ground into small fragments, in the process 

 of mastication. In general we can distinguish in the enteric 

 canal a buccal cavity, a pharynx, an (esophagus or gullet, a 

 stomach, and an intestine. It is in the stomach and anterior 

 part of the intestine that the food becomes acted upon by 

 certain digestive secretions, the effect of which is to render 

 the various ingredients soluble, and thus fitted to be absorbed 

 through the wall of the enteric canal, so as to reach the 

 various parts of the body and supply them with nourish- 



