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a certain hiding-place. Whenever it saw the keeper appear with 

 his net above the tank, it retreated to its corner, while other 

 people it regarded with the greatest calmness and curiosity , 

 swimming about on its side at the top of the water. 



We have now arrived at the true pelagic swimmers , the 

 mackerel. Like the storm-birds and frigate-gulls that spend 

 their lives suspended above the immeasurable plains of ocean, 

 these fish traverse the high seas, only approaching the coast 

 periodically, when (like the tunny) they become the objects of 

 extensive fishing. All attempts to introduce these shy and 

 sensitive fish into the Aquarium have failed. We shall never 

 be able to keep either the tunny or its nearest relative, the 

 sword-fish, in our tanks, for they cannot endure the slightest 

 abridgment of their liberty. They all become frantic and die 

 within a few hours , and only a little fork-mackerel , the 

 beater (Lichia glauca), has, like the Balista, become a re- 

 gular summer guest in the Aquarium. It is an extremely pretty 

 fish, with its slender body shining like pure silver, and its 

 restless activity. 



A pelagic fish akin to the true mackerel, which roves sol- 

 itary in the high seas and is seldom brought to the Aquarium, 

 is the St. Peter's fish (Zeus faber). It derives its name from 

 the legend that out of this fish's mouth St Peter took the piece 

 of money; the people say that the two dark spots on its sides 

 are the impression of the saint's fingers. It swims slowly about, 

 waving its large fins , but refuses all nourishment, and soon 

 turns on its side and dies. It is valued as. food in all European 

 markets. 



The second order of fishes of which we have yet to speak, 

 includes the cartilaginous fishes to which belong the sharks and 

 roaches. Of this group the Aquarium contains almost exclu- 

 sively the ground-fish, which reveal very little of their habits 

 to the visitor. We will therefore chiefly confine our description 

 to the pecularities of their organisation and development, and 

 only in the second place mention their very monotonous habits. 

 Let us first take the sharks. 



The mention of this name usually arouses in the non-scien- 

 tific listener the idea of those sea-giants that are the horror 

 of sailors and all inhabitants of the coast. He is therefore no 



