" FEATHERING " OARS. 15 



IN Art we have invented many similar contrivances, but I 

 believe thar there is not one in which we have not been antici- 

 pated by Nature. Putting aside the insect which has just 

 been described, we have the whole tribe of water- beetles, in 

 which the same principle is carried out in an almost identical 

 manner. In the accompanying illustration, the oar, the rower, 

 and the boat are placed above one another, and next to them 

 are seen one of the oar-legs of the water-boatman and the 

 insect as it appears when swimming on its back. 



Then, there is the foot of the duck, goose, Bwan, and various 

 other aquatic birds, in which the foot presents a broad blade 

 as it strikes against the water, and a narrow edge as it recovers 

 from the stroke. Some 5 oars ago, a steam yacht was built 

 and propelled by feet made on the model of those of the swan. 

 She was a very pretty vessel, but art could not equal nature, 

 and at present the swan-foot propeller, however perfect in 

 theory, has not succeeded in action. Perhaps, if some nautical 

 engineer were to take it in hand, he would procure the desired 

 result. 



Almost exactly similar is the mode of propulsion employed 

 by the lobster, the prawns and shrimps, their tails expanding 

 widely into a fan-like shape as they strike against the water, 

 and then collnpsing when the stroke is withdrawn, so as to 

 allow them to pass through the water with the least possible 

 resistance. 



The same principle is to be seen in the lively little Acaleph, 

 for which there is unfortunately no popular name, and which 

 we must therefore call by its scientific title of CYDiPrE, or 

 Beroe, these names being almost indifferently used. When full 

 rown, it is about as large as an acorn, and very much of the 

 same shape. It is as transparent as if made of glass, and, w r hen 

 in the water, is only visible to practised eyes. 



En passant, I may remark that the familiar term of " water," 

 when applied to diamonds, is owing to their appearance when 

 placed in distilled water. Those which can be at once 

 seen are called stones of the second water. Those which 

 cannot be seen, because their refractive powers are equal to 

 those of the water, are called "diamonds of the first water," 

 and are very much more valuable than the others. 



4-8 the Cydippe is, in fact, little more than sea- water, 



