INFUSORIANS. 



5<53 



mail-coated flagellata (highly magnified). 



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- 

 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 on calm warm 

 nights when there has been a gentle sea - breeze for 

 several days. This strange phenomenon has attracted 

 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 



PHOSPHORESCENT ANIMALCULE, 



Noctiluca (magnified 150 

 diameters). 



