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Chapter VI. 



PREPARATION OF FOOD. 



^ 1 . Prehension of Liquid Food. 



In studying the series of processes which con- 

 stitute assimilation, our attention is first to be 

 directed to the mode in which the food is in- 

 troduced into the body, and to the mechanical 

 changes it is made to undergo before it is sub- 

 jected to the chemical action of the digestive 

 organs. The nature of these preliminary pro- 

 cesses will, of course, vary according to the tex- 

 ture and mechanical condition of the food. Where 

 it is already in a fluid state, mastication is unne- 

 cessary, 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 Hydatid, for instance, has four sucking 

 apertures disposed round the head of the animal : 



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

 three, six, or more sucking disks, by which they adhere to sur- 

 faces : to these animals the names Distoma, Tristoma, Hexas- 

 toma, and Polystorna have been given ; but these denominations, 

 implying a plurality of mouths, are evidently incorrect, since the 



VOL. II. I 



