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 (= 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 1 



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 carefully the vortices, or whirlpools, which are so 

 vigorously circling round 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 

 ventral 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 clown this gulf. Yet not all, nor nearly 



