DIFFERENT WAYS OF SWIMMING 



accustomed upon land. They are excited by what they 

 see, exchange impressions, go away regretfully and are 

 always glad to come back again. The tanks of living 

 fish attract crowds of visitors who are certainly not 

 specialists. The novelty delights these visitors, who 

 now see as they are in life creatures of which they 

 have hitherto known nothing except that they are 

 good to eat. They can hardly tear themselves away. 

 There is always something new to see; a change of 

 position, an alteration in colour, re-awakens their atten- 

 tion immediately it begins to tire. The aquarium is 

 a perpetual kaleidoscope, a continual attraction to the 

 layman, a source of sustained interest to the naturalist 

 observer. 



The fish may be placed in two categories: those 

 which are always swimming and those which swim 

 only occasionally. The former keep well away from 

 the sides of the tank; come and go, rise and descend, 

 continually on the move, though their speed varies. 

 Sometimes they maintain themselves for a moment 

 in a state of equilibrium, but they seldom go down 

 and stay on the bottom for any length of time. The 

 occasional swimmers follow exactly the opposite course: 

 they often settle; they partly cover the floor of the 

 tank, and there stay motionless, more or less per- 

 manently, coming out of their inertia at intervals to 

 swim for a few moments, then fall back and rest 

 once more. 



The first category, the sea perches, mullets, the sea 

 breams known as gilt-heads, sargo and many others 

 like them, swim with their pectoral and caudal fins. 

 They have two speeds and two propellers, one for 

 ordinary and one for occasional use only. Usually, 

 they beat the water with their two pectorals like two 

 oars, and, according to the rhythm of these strokes, 

 their frequency and force, they move forward, either 

 slowly or quickly, the caudal fin, in this case, acting 

 simply as a rudder. They move in all directions, turn 



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