NUTRITION IN THE INFUSORIA. 95 



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 dis- 

 tinguished 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 

 transparent, becomes dotted with a number of 

 distinctly circular spots, of a dark blue colour, 

 evidently produced by particles of indigo accu- 

 mulated in those situations. In some species, 

 particularly those which have a contracted part, 

 or neck, between the head and the body, as the 

 Rotifer vulgaris, these particles can be traced 

 in a continuous line in their progress from the 

 mouth to these internal cavities. 



In this way, by the employment of colouring- 

 matters, Ehrenberg succeeded in ascertaining 

 the existence of a system of digestive cavities 

 in all the known genera of this tribe of animals. 

 There is now, therefore, no reason for admitting 

 that cuticular absorption of nutritive matter ever 

 takes place among this order of beings. Whole 

 generations of these transparent gelatinous ani- 

 malcules may remain immersed for weeks in an 

 indigo solution, without presenting any coloured 

 points in their tissue, except the circumscribed 

 cavities above described. 



Great variety is found to exist in the forms, 



