n ANIMALS AND PLANTS 255 



of the frog (Part I, Chap. VII) are not provided with a 

 cellulose cell-wall and do not contain chlorophyll. It is 

 characteristic, on the other hand, of most plant-cells 

 which also consist of nucleated protoplasm that they 

 are surrounded 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 move- 

 ments 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 " king- 

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



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

 resting condition ; it ingests solid proteids, its nutrition 

 being therefore holozoic : it has a contractile vacuole : 

 and it performs 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. though not distinct in 

 S. pluvial is : and its movements are ciliary. 



Euglena has a cellulose wall in the encysted state : in 

 virtue of its chlorophyll it is nourished by the absorption 

 of carbon dioxide and mineral salts, but it may also ingest 

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



