3538 THE LOWEST ANIMALS 



so named were classed with the worms and radiated animals or zoophytes. As the 

 microscope improved, infusorians were found to possess a considerable amount of 

 structure. Ehrenberg attributed to them a highly complex organization, supposing 

 them to possess intestines, nervous system, etc. Later observations negatived 

 these views, and showed them to be animals formed of one cell or composed of a 

 colony of one-celled individuals. It is true that this cell, or unit mass of proto- 

 plasm, may show a wonderful amount of differentiation, what with its nucleus, con- 

 tractile vacuole, mouth and gullet, its variously arranged cilia or flagella, its con- 

 tractile fibres, its separation into an outer denser and an inner more fluid proto- 

 plasm, and its horny cups, stalks, etc. Most of the species here described live in 

 ponds and ditches, the larger forms preferring clear to stagnant and muddy water. 



FLAGELLATED INFUSORIANS Order FLAGELLATA 



The characteristic of the group is the possession of one or two flagella, or small 

 whip-like appendages, at the base of which is an opening in the denser surface 

 layer of protoplasm; a nucleus and contractile vacuoles are present, and frequently 

 a brilliant red spot of pigment, known as the eye-spot. The Monads, which are 



the simplest members of the group, are 

 common in fresh water and in infusions; 

 typical forms consisting of a spherical 

 or oval cell provided with a flagellum. 

 Some species contain chlorophyll, and are 

 claimed by the botanists. The common 

 Volvox, for instance, which forms a green- 

 colored, spherical colony of monad cells 

 has been described as a plant and also as 

 an animal by botanists and zoologists 

 MAIL-COATED FLAGELLATA. respectively. The animal and vegetable 



(Highly magnified.) kingdoms converge downward toward a 



common point, at which it is difficult to 



say whether the manifestations of the physical basis of life i.e. protoplasm are 

 such as we ascribe to plant life or to animal life. In the case of Volvox, the pres- 

 ence of chlorophyll would at first sight seem to stamp the organism as a plant; but 

 the phases of life history are rather those of an animal organism. The collared 

 group possess cup-like collars, and they frequently secrete horny receptacles or 

 cups, which may form elegant tree-like colonies. 



The mail-coated group are of very varied form, the body being often pro- 

 longed into long spiny processes. From the presence of cellulose in the cell wall, 

 and of chlorophyll in the body substance, the proper position for these organisms 

 would appear to be the vegetable kingdom, but taking their general life history 

 into consideration they may be regarded as animal organisms. They possess two 

 large flagella which fit into grooves. Ceratium tripos (often looked upon as 

 an alga), which sometimes forms chains of twenty or more individuals, is phos- 

 phorescent. 



