COMPLEX APPARATUS FOR NUTRITION. 101 



quickly, and must repeatedly throw off its integu- 

 ments during its continuance in the larva state, 

 consumes a vast quantity of food compared with 

 the size of its body ; and hence we find it provided 

 with a digestive apparatus of considerable size. 



Chapter VI. 



PREPARATION OF FOOD. 



§ 1 . Prehension of Liquid Food. 



In studying the series of processes which constitute 

 assimilation, our attention is first to be directed to 

 the mode in which the food is introduced into the 

 body, and to the mechanical changes it is made to 

 undergo before it is subjected to the chemical 

 action of the digestive organs. The nature of these 

 preliminary processes will, of course, vary according 

 to the texture and mechanical condition of the food. 

 Where it is already in a fluid state, mastication is 

 unnecessary, and the receiving organs consist 

 simply of an apparatus for suction. This is the 

 case very generally with the Entozoa, which subsist 

 upon the juices of other animals, and which are all 

 provided with one or more sucking orifices, often 

 extended in the form of a tube or proboscis.* The 



* Some species of Fasciolce, or flukes, are furnished with two, 

 three, six, or more sucking disks, by which they adhere to surfaces : 

 to these animals the names Distoma, Tristoma, Hexastoma, and 

 Polystoyna have been given ; but these denominations, implying a 

 plurahty of mouths, are evidently incorrect, since the sucking disks 



