48 THE HISTORT OF CREATION. 



dictions are not altogether caused by our imperfect know- 

 ledge of the Protista, but in reality by their true nature. 

 Indeed, most Protista present such a confused mixture of 

 several animal and vegetable characteristics, that each in- 

 vestigator may arbitrarily assign them either to the animal 

 or vegetable kingdom. Accordingly as he defines these 

 two kingdoms, and as he looks upon this or that cha- 

 racteristic as determining the animal or vegetable nature, 

 he will assign the individual classes of Protista in one case 

 to the animal and in another to the vegetable kingdom. But 

 this systematic difficulty has become an inextricable knot 

 by the fact that all more recent investigations on the lowest 

 organisms have completely effaced, or at least destroyed, the 

 sharp boundary between the animal and vegetable king- 

 dom which had hitherto existed, and to such a degree that 

 its restoration is possible only by means of a completely 

 artificial definition of the two kingdoms. But this defini- 

 tion could not be made so as to apply to many of the 

 Protista. 



For this and other reasons it is, in the mean time, best 

 to exclude the doubtful beings from the animal as well 

 as from the vegetable kingdom, and to comprise them in a 

 third organic kingdom standing midway between the two 

 others. This intermediate kingdom I have established as 

 the Kingdom of the Primary Creatures (Protista), when 

 discussing general anatomy in the first volume of my 

 General Morphology, p. 191-238. In my MonogTaph of 

 the Monera,^^ I have recently treated of this kingdom, 

 having somewhat changed its limits, and given it a moi'e 

 accurate definition. Of independent classes of the kingdom 

 Protista, we may at present distinguish the following: — 



