84 THE VITAL FUNCTIONS. 



of a highly attenuated solution of this substance is 

 applied to a drop of water in which are some 

 pedunculated Vorticellae, occupying the field of the 

 microscope, the most beautiful phenomena present 

 themselves to the eye. Currents are excited in all 

 directions by the vibrations of the cilia, situated 

 round the mouths of these animalcules, and are 

 readily distinguished by the motions of the minute 

 particles of indigo which are carried along with 

 them ; the currents generally all converging towards 

 the orifice of the mouth. Presently the body of 

 the vorticella, which had been hitherto quite trans- 

 parent, becomes dotted with a number of distinctly 

 circular spots, of a dark blue colour, evidently 

 produced by particles of indigo accumulated in 

 those situations. In some species, particularly 

 those which have a contracted part, or neck, be- 

 tween the head and the body, as the Rotifer vul- 

 garis, these particles may be traced in a continuous 

 line in their progress from the mouth, through the 

 neck, into the internal cavities. 



Following up this train of observations, Ehren- 

 berg persuaded himself that he had discovered not 

 only the existence of a system of digestive cavities 

 in all the known genera of this tribe of animals ; 

 but that he could also trace out their forms, situa- 

 tions, and arrangement. They appeared to exhibit 

 great variety of structure in the different tribes; 

 but without any obvious relation to the form or 

 magnitude of the animalcule. The Monas atomus, 

 the minutest of the whole tribe, presented a number 

 of sacs, opening by as many separate orifices, from 

 a circumscribed part of the surface. In others, as 



