154 THE STORY OF FISH LIFE. 



in some cases by its degeneration, and in others 

 by its transformation into an organ of prehension 

 and weapon of offence. Thus in some of the 

 eagle-rays of the genus JElobates, it has assumed 

 the form of a long trailing and very slender 

 whip-lash armed with spines, the whole forming 

 a very formidable weapon indeed, as will be seen 

 presently. In the genus Urolojyhus the tail is 

 short, and armed with but a single spine. Eagle- 

 rays appear occasionally off the coast of Scotland. 

 " They frequently arrive suddenly in oyster-beds, 

 to the dismay of the owners, where they remain 

 so long as any of the molluscs are obtainable." 

 Mr Day, in describing the spine-tailed rays, says 

 "they lie concealed in the sand, and are reputed 

 to be able to suddenly encircle fish, or other prey 

 swimming above them, with their long whip-like 

 tails, and wound them with their serrated tail 

 spines." 



The possession oi spines is common to many 

 fishes. Their earliest appearance is in the form 

 of supports to the fins. But, as we have just 

 seen, their original function may be lost, and the 

 spine by a very natural transition becomes a 

 weapon of offence. In its new role, however, 

 the spine undergoes further modification, and 

 adds to its dread powers the sting of poison. 

 The evolution of this poison organ is, we shall 

 see, as gradual as is the rise and development of 

 all other organs 



The spines in the tail of uElobates may be 

 five in number, and are s^atid on the upper 

 surface of the tail ; all are barbed, and in con- 

 sequence inflict a very dangerous wound. " Al- 



