2l8 COMPARATIVE ZOOLOGY 



Owen, propose a fourth " kingdom," that of the 

 Protista, to receive those living beings which are 

 organic, but not distinctly vegetable or animal. But a 

 greater difficulty arises in attempting to fix its precise 

 limits. 



The drift of modern research points to this : that 

 there are but two kingdoms of nature, the mineral and 

 the organized, and these closely linked together ; that 

 the latter must be taken as one whole, from which two 

 great branches rise and diverge. " There is at bottom 

 but one life, which is the whole life of some creatures 

 and the common basis of the life of all ; a life of sim- 

 plest moving and feeling, of feeding and breathing, of 

 producing its kind and lasting its day : a life which, so 

 far as we at present know, has no need of such parts 

 as we call organs. Upon this general foundation are 

 built up the manifold special characters of animal and 

 vegetable existence ; but the tendency, the endeavor, so 

 to speak, of the plant is one, of the animal is another, 

 and the unlikeness between them widens the higher the 

 building is carried up. As we pass along the series of 

 either [branch] from low to high, the plant becomes 

 more vegetative, the animal more animal." 64 



Defining animals and plants by their prominent char- 

 acteristics, we may say that a living being which has 

 cell walls of cellulose, and by deoxidation and synthesis 

 of its simple food stuffs produces the complicated or- 

 ganic substances, is a plant ; while a living being which 

 has albuminous tissues, and by oxidation and analysis 

 reduces its complicated food stuffs to a simpler form, 

 is an animal. But both definitions are defective, includ- 

 ing too many forms, and excluding forms that properly 

 belong to the respective kingdoms. No definition is 

 possible which shall include all animals and exclude all 

 plants, or vice versa. 



