THE STUDY OF MOVEMENT 27 



families of fish are those in which, as in mackerel or 

 tunny, the art of swimming is most masterly. Am- 

 phibia, that lie motionless for long intervals, have 

 remained stationary in the scale of being, whilst 

 reptiles, though capable of the most rapid running, 

 gliding, and striking movements, are, owing to their fre- 

 quent lethargy, only mediocre vertebrates, surpassed 

 by both mammals and birds, which in virtue of their 

 more sustained activity have attained the premier 

 position. 



There is an aesthetic side to the movements of 

 animals that makes us never tire of the spectacle. 

 The ease with which fish and porpoises advance, turn, 

 and press onwards under a sudden impulse, the sense 

 of restrained strength in the taut muscles of a horse 

 or dog, the freedom and masterliness of flight, the 

 graceful form and manifold rich colouring of birds, 

 lend inexhaustible attraction to the study of motion. 



The energy of many animals has something of that 

 enduring and periodically varying quality that belongs 

 to river, wind, and sea. Gulls and albatross follow 

 in the wake of vessels for days, and even weeks, with 

 no sign of weariness, sleeping on the water and only 

 stooping to feed. Fish when not in active move- 

 ment are untiringly adjusting their balance by small 

 muscular contractions. The beating of the heart, on 

 which all other motion depends, endures night and 

 day, and exhibits a rhythm of diurnal quickening and 

 nocturnal slackening which is symbolic of the flow 

 and ebb that rules living and inanimate nature. 



