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 diffixsion). 



The Wliip-siuim'niers (Flagellata), which we consider as a 

 third class of the kingdom Protista, are of no less doubtful 

 nature than the Amoebfe. They often show as close and 

 important relations to the vegetable as to the animal 

 kingdom. Some Flagellata at an early stage, when freely 

 moving about, cannot be distinguished from real plants, 

 especially from the spores of many Algse ; whereas others 

 are directly allied to real animals, namely, to the fringed 



Fig. 11. — A single Whip-swimmer (Englena 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 

 cells which live in fresh or salt water, either 

 singly or united in colonies. The characteristic 

 part of their body is a very movable simple 

 or compound whip-like appendage (whip, or 

 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 Euglenae, immense masses of 

 which frequently make our ponds in spring quite green. 



