226 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



COMPARISON OF THE GASTRO-INTESTINAL Mucous SURFACES WITH THAT OF 



THE SKIN. 



II. PREHENSION OF FOOD. 



1. PREHENSION OF SOLIDS. By the term prehension of food is meant 

 the different methods emplo3 T ed by animals in seizing their food and 

 conveying it to the oral aperture of their alimentary canal. Man} T aquatic 

 animals, whose food consists of small particles diffused through water, 

 are supplied with an apparatus for producing currents so as to bring 

 such substances within their reach. This is especial^ true in the case 

 of fixed forms of life which are unable to go in search of their food. 

 Thus, the sponge and sea-mat, and various other of the lower forms of 

 life, obtain their nourishment by the production of currents in the water 

 through the vibration of cilia lining or surrounding the opening of their 

 alimentary canal. In infusoria, also, we find similar arrangements, 



