16 STUDIES IN ANIMAL LIFE, 



Observe how transparent it is, and with what 

 easy, undulating grace it swims about; yet this 

 swimmer has no arms, no legs, no tail, no backbone 

 to serve as a fulcrum to moving muscles nay, it has 

 no muscles to move with. "Pis a creature of the 

 most absolute abnegations sans eyes, sans teeth, 

 sans every thing ; no, not sans every thing, for, as 

 we look attentively, we see certain currents pro- 

 duced in the liquid, and, on applying a higher mag- 

 nifying power, we detect how these currents are 

 produced. All over the surface of the Opalina 

 there are delicate hairs in incessant vibration ; these 

 are the cilia* They lash the water, and the animal 

 is propelled by their strokes, as a galley by its hund- 

 red oars. This is your first sight of that ciliary ac- 

 tion of which you have so often read, and which 

 you will henceforth find performing some important 

 service in almost every animal you examine. Some- 

 times the cilia act as instruments of locomotion; 

 sometimes as instruments of respiration, by contin- 

 ually renewing the current of water ; sometimes as 

 the means of drawing in food, for which purpose 

 they surround the mouth, and by their incessant 

 action produce a small whirlpool into which the 

 food is sucked. An example of this is seen in the 

 Yorticella. (Fig. 2.) 



Having studied the action of these cilia in micro- 

 .scopic animals, you will be prepared to understand 

 their office in your own organism. The lining 



* From cilium, a hair. 



