INFUSORIANS. 
563 
Flagellated Infusorians,—O rder Flagellata. 
MAIL-COATED flagellata (highly magnified). 
'Tlie 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- 
coloured, spherical colony of monad cells 
has been described as a plant and also as 
an animal by botanists and zoologists 
respectively. The animal and vegetable 
kingdoms converge downwards towards 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 presence 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 phosphorescent. 
On calm dark nights during the summer and autumn 
the surface of the sea is occasionally seen to be per¬ 
vaded by a beautiful bluish or greenish luminosity. 
The appearance of the phosphorescence is somewhat 
capricious, but it will best be seen 011 calm warm 
nights when there has been a gentle sea - breeze for 
phosphorescent animalcule, several days. This strange phenomenon has attracted 
Noctiluca (magnified 150 ,, .. P , ., . . 
diameters) attention from the earliest times, but it was not till 
the middle of the last century that the cause was dis¬ 
covered. The luminosity is in most cases due to the presence of multitudes 
of tiny jelly-spheres, each smaller than a pin’s head. On taking up a tumbler 
of the sea water, the spheres frequently form a thick layer at the surface. By 
separating a few of the organisms on blotting - paper, the light emitted will 
