WHEEL-BEARERS. 231 



all ; for the lips appear to possess the sense of taste, or of 

 some modification of touch, which enables them to refuse or 

 to receive the atoms presented to them, so that only such 

 particles pass down the throat as are selected for food. 

 Some of the atoms of pigment are admitted, and one of 

 the most pleasing sights connected with these animals, is 

 to watch the swallowing of coloured food, its reception 

 into the singular sunken mouth, where the great powerful 

 jaws act upon it : thence its dismissal through the gullet, 

 where certain glands pour upon it their secretions,, into 

 the stomach, where other glands, answering to a liver, 

 change it, and thence into the intestine and rectum, until 

 its indigestible portion is discharged through the cloacal 

 orifice. 



The object of the mingling of colour with the water in 

 which these and similar animals are held for observation, 

 was the tracing of the phenomena of digestion. And, in- 

 deed, it renders the whole process beautifully distinct ; 

 for, from the transparency of the tissues, the presence of 

 the coloured pellet is everywhere recognisable, since it 

 retains its form and hue under all its changes, clearly 

 revealing to us the shape, dimensions, and directions of 

 the various canals through which it passes ; here and there 

 diffusing throughout the viscus in which it is held a beau- 

 tiful roseate hue, more or less deep, without, however, 

 losing its own definite outline. 



Let me now direct your attention to the organs devoted 

 to the seizing and mastication of the food. And the more, 

 because the form of these organs in the Rotifera is quite 

 peculiar, quite unlike what is found in any other class of 

 animals ; though the parts are essentially the same as 

 those which we have already seen entering into the mouth 

 in insects. 



Eemoving the carmine-stained water, I put into the 

 live-box a drop from a vase very rich in organisms of 

 many kinds. Among these you see very numerous the 



