DIFFERENT WAYS OF SWIMMING 



oars. These fins have not the suppleness or the undu- 

 lating grace of those of the skate; they are narrowly- 

 jointed to the body instead of confluent with it, 

 supported by ribs which stand out and are quite stiff. 

 Their only advantage is their fullness, which allows 

 of their being used as paddles and, in certain species, 

 the variety of their tint and the beauty of their colouring. 

 Compared with the skate's fin, the tool is of the same 

 type, but made on an entirely different plan. 



The flying gurnards follow this model, but in an 

 exaggerated way and in another respect. They some- 

 times settle on the bottom, but more often they swim 

 about in the water of the tank, using their tails as sculls, 

 and forcing their way to the top. As they approach 

 the surface, they spread their pectorals, which are 

 broader and longer than those of the typical gurnards, 

 since, when fully extended, their combined spread 

 exceeds the length of the body. They extend these 

 fins, but they cannot use them effectively as swimming 

 paddles, because they are too big for the muscles 

 which activate them. The resistance offered by the 

 water — the arm of the lever being too long — exceeds 

 the power of the motor. These unusually broad fins 

 are not much use as propellers through the water 

 because of their very size; at most they serve as 

 balancers in the water, the sole propeller being the 

 scull formed by the tail. We may observe, however, 

 in the fishes' behaviour under water the preparations 

 for their planing flight when they succeed in lifting 

 themselves above the surface. They give the first 

 impulse by vigorous strokes of the caudal fin, shoot 

 obliquely upwards from the depths, spread their 

 pectorals as great flat balancers and, coming out of 

 the water, are carried on by the speed they have 

 already attained, and are held up in the air by these 

 balancers which act as planes until the force of gravity 

 brings them back into the sea from which they sprang. 



In a corner of the tank a few seahorses with pre- 



47 



