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 certain 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 external 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 pounded up 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 



