48 THE HISTORY 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 Monograph of 
the Monera,® I have recently treated of this kingdom, 
having somewhat changed its limits, and given it a more 
accurate definition. Of independent classes of the kingdom 
Protista, we may at present distinguish the following :— 
