230 EVENINGS AT THE MICROSCOPE. 



The Brachionus is the boat, its cilia are the oars, and 

 its foot is the rope. As long as this last maintains its 

 hold, the whole force of the ciliary stroke is spent on the 

 water, and currents are the result; but as soon as this 

 hold is broken, the force acts on the animal (=z boat), 

 which is thus rowed rapidly forwards. 



The use of the cilia in this latter case is obvious. They 

 enable the little animal to rove about at its wayward will ; 

 and doubtless motion is as pleasant and necessary to it as 

 to the fish in the sea, or to the bird in the air. But what 

 is the object of their vigorous rotation, when the animal 

 chooses to maintain a firm hold with its foot ? What is 

 the use of rowing a boat, if you do not choose to let go 

 the painter ? 



To solve this enigma, let us search up our little Brachion 

 once more ; he will not roam long before he settles soberly 

 again. Yes, here I have him moored. Now, mark care- 

 fully the vortices, or whirlpools, which are so vigorously 

 circling around the animal's front, and you will perceive 

 that the movement is not a strictly circular one, but that 

 each whirlpool has an outlet close to the cilia ; for the 

 accumulated and condensed particles of pigment, after many 

 rotations, pass off in an united stream between the two 

 crowns, and go away horizontally in a line from the ven- 

 tral side of the front. That is to say, each vortex pours 

 off its accumulation at a point on the inner side of the 

 ciliary circle, and the two streams, uniting, pass off from 

 the lip of the shell, to be drawn in again, however, by-and- 

 by, when the centrifugal force is exhausted. 



Now this stream passes immediately over the mouth, 

 which is an opening in the flesh of the front, forming a 

 deep cleft on the ventral side, the lips of which, as also 

 the whole interior of the tube, of which it is the orifice, 

 are richly covered with cilia. A certain portion of the 

 atoms are thus arrested by these cilia, and are hurled by 

 their vibrations down this gulf. Yet not all, nor nearly 



