THE PROTISTA, 47 
must be connected at their lowest root, and likewise the 
three or six main classes, or phyla, of the vegetable kingdom 
must be traced to a common and most ancient original form. 
How the connection of these tribes is to be conceived I shall 
explain in the succeeding chapters. But before proceeding to 
this, we must occupy ourselves with a very remarkable group 
of organisms, which cannot without artificial constraint be 
assigned either to the pedigree of the vegetable or to that of 
the animal kingdom. These interesting and important 
organisms are the primary creatures, or Protista. 
All organisms which we comprise under the name of 
Protista show in their external form, in their inner struc- 
ture, and in all their vital phenomena, such a remarkable 
mixture of animal and vegetable properties, that they cannot 
with perfect justice be assigned either to the animal or to 
the vegetable kingdom; and for more than twenty years an 
endless and fruitless dispute has been carried on as to 
whether they are to be assigned to this or that kingdom. 
Most of the Protista are so small that they can scarcely, if 
at all, be perceived with the naked eye. Hence the ma- 
jority of them have only become known during the last 
fifty years, since by the help of the improved and general 
use of the microscope these. minute organisms have been 
more frequently observed and more accurately examined. 
However, no sooner were they better known than endless 
disputes arose about their real nature and their position in 
the natural system of organisms. Many of these doubtful 
primary creatures botanists defined as animals, and zoolo- 
gists as plants; neither of the two would own them. Others, 
again, were declared by botanists to be plants, and by 
zoologists to be animals ; each claimed them. These contra- 
