II ANIMALS AND PLANTS 255 



also consist of nucleated protoplasm that they are sur- 

 rounded with a cellulose cell-wall, and that, in the case of 

 green plants, they contain chlorophyll. Speaking generally, 

 the nutrition of animals is holozoic, and that of green plants 

 holophytic ; and in correspondence with this difference in 

 the character of the food, most animals have an ingestive 

 aperture or mouth for taking in the solid food, and some 

 kind of digestive cavity, either permanent (stomach), or 

 temporary (food-vacuole) ; they also have, as a rule, some 

 kind of excretory apparatus. Moreover, animals are usually 

 capable of automatic movement, while in most plants the 

 organism, as a whole, exhibits no automatism, but only the 

 slow movements of growth. 



Let us now apply these definitions to the simple forms 

 described above and see how far they will help us in placing 

 those organisms in one or other of the two " kingdoms " 

 (p. 220) into which living things are divided. 



Amoeba has a cell-wall, probably nitrogenous, in the rest- 

 ing condition : it ingests solid proteids, its nutrition being 

 therefore holozoic : it has a contractile vacuole : and it per- 

 orms amoeboid movements. It may therefore be safely 

 considered as an animal. 



Sphaerella has a cellulose wall that contains chlorophyll and 

 its nutrition is purely holophytic : a contractile vacuole is 

 present in S. lacustris but absent in S. pluvialis : and its 

 movements are ciliary. 



Euglena has a cellulose wall in the encys-ted state : in 

 virtue of its chlorophyll it is nourished by the absorption of 

 carbon dioxide and mineral salts, but it can also ingest solid 

 food through a special mouth and gullet : it has a contractile 

 vacuole, and performs both euglenoid and ciliary movements. 



In both these organisms we evidently have conflicting 



