MECHANISM OF NUTRITION 73 



glossus "). Dr Gaskell * has reversed the position 

 by the recent statement that a large number 

 of zoologists, who consider the notochord as a 

 great characteristic of the vertebrate organisa- 

 tion, have followed Bateson in the matter of 

 terminology. 



Taken as a whole the habits of animals are 

 cast into certain well-defined moulds, and it is 

 quite easy to understand why this should be 

 so ; but the much more apparent than real 

 simplicity of the matter is no reason why it 

 should not be stated at length. Animals differ 

 from plants in their nutrition, mobility, and 

 sensibility. The manner in which the nutrition 

 of animals differs from that of green plants is 

 sharp and unequivocal, so much so that it can 

 be expressed in two contrasting terms, holozoic 

 and holophytic, between which extremes, how- 

 ever, all grades of what is known as mixotrophism 

 (mixed dietary) are to be found, chiefly but 

 not entirely amongst the lower orders. 



Green plants alone can elaborate their own 

 food, with the help of the sun, from inorganic 

 substances ; animals require their food ready 

 made before they can begin to assimilate it. 

 Plants have only to assimilate, and that in one 

 way ; animals have first to procure their food, 

 and that in many ways. And yet there is as 



1 W. H. Gaskell, ''Origin of Vertebrates," London, 1908, see 

 p. 16. 



