WAVE-CtTBEENTS ON SHALLOW-SEA FAUNAS. 271 



sand sufficient to cover the bottom, it will be seen how indifferent 

 they are to oscillating currents, and how easily they evade them. 

 They meet the danger either by flashing with great velocity under 

 the sand, or by passive resistance, lying quite still whilst the 

 sand-ripples formed by the rocking of the water cover tliem up. 

 It has been thought that flat-fish cover themselves with sand for 

 the purpose of concealment ; but this hypothesis fails to meet the 

 fact that among them are included many varieties, such as the 

 halibut and skate, that grow to a large size, and can scarcely need 

 to hide themselves from living foes. Moreover, such concealment 

 cannot be assured to the feeblest of them, as the smallest and 

 weakest have to move about after their own prey. Further, as 

 the peculiar habit of swimming on the side, and the peculiar posi- 

 tion of the eyes on the same side of the head, are not conge- 

 nital, but acquired after the young are hatched, the latter when 

 most exposed to be devoured by fish have not the benefit of the 

 hypothetical means of protection from these enemies. On the 

 other hand, when we see that these peculiar forms and habits 

 afi'ord a perfect protection against wave-currents, it seems rea- 

 sonable to conclude that the said forms and habits have a very 

 close connexion with the special dangers against which they are 

 manifestly such efficient safeguards*. 



Many of the visitors to the Southport Aquarium during the 

 visit of the British Association in 1883 watched with interest the 

 struggles of the king crabs {Limulus) to regain their normal 

 position, when, by climbing the walls of their tank, they had fallen 

 on their backs. It seemed anomalous that a crustacean should 

 be so constituted as to be helpless in any position in its native 

 element. Owing to the hemispherical form of the carapace of 

 these crustaceans, no such difficulty would be experienced on an 

 open coast in shallow water, as gentle wave-currents would suffice 

 to restore them to position if by any chance upset. 



* Note. — The following statement of Professor Moseley seems exactly in 

 point: — ". . . the young flat fish termed PlatessEe . . . are often taken in the open 

 ocean ; and it appears probable that when there placed under unnatural circum- 

 stances, their de-velopment becomes arrested, and many probably perish even- 

 tually .... without the arrangement of their eyes ever becoming unsymmetrical. 

 The deep sea is devoid of flat fish" .... (Nature, vol. xxvi. p. 563). It seems 

 clear from the above that the horizontal position, unsymmetrical eyes, and 

 quasi-burrowing habits of flat fish are peculiarities connected with their shallow- 

 water habitats, and with them alone. — A. K. H. 



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