106 LIFE IN THE SEA [CH. 



many parasites outside the body of other animals in 

 artificially prepared juices or jellies; thus many 

 species of bacteria may live either in the body of a 

 host or in the sea- water or mud, but their mode of 

 nutrition is the same in each case. 



Are there animals which live in the open and 

 which do not ingest solid food in the shape of the 

 bodies of other animals and plants, but live by 

 ingesting matter which is dissolved in the sea-water ; 

 in short are there marine animals which do not eat 

 visible food ? Now it is not at all remarkable that 

 zoologists, whose attention is usually concentrated 

 on the study of form rather than function who 

 look on an organism not so much as ' something 

 happening,' but as a structure of skeleton, muscles, 

 alimentary canal, glands, nervous system, etc. 

 should have regarded such a mode of nutrition as 

 improbable. Why should an animal possess an ali- 

 mentary canal and glands if these structures are 

 not for the purpose of the digestion of food ? Yet 

 the study of parasitism and its modifications should 

 have led us to postulate the existence of a wide- 

 spread saprozoic mode of nutrition, at all events 

 among the lower marine animals. We might not 

 have expected to find it among the terrestrial 

 animals but where an organism lives continually 

 bathed in a liquid medium, the absorption of food 

 matter through its outer surface apart altogether 



