16 



NATURE S TEACHINGS. 



entangled in the slightest imaginable and most transparent 

 tissue of animal fibre, it is evident that the water and the 

 Cydippe must be of almost equal refracting power, and that 

 therefore the acaleph must be as invisible as diamonds of the 

 "first water." Indeed, I have often had specimens in a glass 

 jar which were absolutely invisible to persons to whom I wished 

 to show them. 



But an experienced eye detects the creature at once. Along 

 its body, at equal distances, are eight narrow bands, over 

 which the colours of the rainbow are, though very faint, per- 

 petually rippling. This appearance is caused by the machinery 

 which impels the body, and which seems never to cease. Each 

 of these bands is composed of a vast number of tiny flaps, which 

 move up and down in regular succession, so as to cause the 

 light to play on their surfaces. And, as they move as if set on 

 hinges, they of course offer no resistance to the water after 

 their stroke is made. 



Now let us compare these works of nature with those of art. 

 We have already seen the parallels of the oar, and we now come 



CYDIPPE AND 



PADDLES. 



PRAWN SWIMMING. 

 FEET OP DUCK. 



SELF-FEATHERING PADDLE-WHEEL. 



to those of the paddle-wheel. "When paddle-steamers were 

 first invented, the blades were fixed and projected from the 

 wheel, as if they had been continuations of its spokes. It was 

 found, however, that a great waste of power, together with 

 much inconvenience, was caused by this arrangement. Not 



