THE FLAGELLATA. 57 
colourless blood-cells; whereas the most ancient single- 
celled plants encased by their membranes were no longer 
able to do this, and could admit through it only fluid 
nutrition (by means of diffusion). 
The Whip-swimmers (Flagellata), which we consider as a 
third class of the kingdom Protista, are of no less doubtful 
nature than the Amcebee. They often show as close and 
important relations to the vegetable as to the animal 
kingdom. Some Ilagellata at an early stage, when freely 
moving about, cannot be distinguished from real plants, 
especially from the spores of many Algz; whereas others 
are directly allied to real animals, namely, to the fringed 
Fic. L1.—A single Whip-swimmer (Euglena striata), greatly 
magnified. Above a thread-like lashing whip is visible; in 
the centre the round cellular kernel, with its kernel speck. 
Infusoria (Ciliata). The Flagellata are simple 
y ye cells which live in fresh or salt water, either 
iid) singly or united in colonies. The characteristic 
Wepwes part of their body is a very movable simple 
Vit 
or compound whip-lke appendage (whip, or 
Nay 
flagellum) by means of which they actively 
swim about in the water. This class is divided 
into two orders. Among the fringed whip- 
swimmers (Cilioflagellata) there exists, in addition to the 
long whip, a short fringe of vibrating hairs, which is wanting 
in the unfringed whip-swimmers (Nudoflagellata). To the 
former belong the flint-shelled yellow Peridinia, which are 
largely active in causing the phosphorescence of the sea; to 
the latter belong the green Euglenze, immense masses of 
which frequently make our ponds in spring quite green. 
