THE SHARKS AND RAYS 89 



immensely long upper lobe of the tail fin. This is in some 

 examples even longer than the head and body together, and is 

 normally as long, and it dwarfs every other feature of this 

 shark, for its head and body, its second dorsal and anal 

 fins, its gill-openings, its spiracles, and its teeth are all com- 

 paratively small. A thresher shark, measuring 13 ft. 10 in. 

 (of which the tail took up close on 7 ft.), was found 

 in the Firth of Forth in August, 1899, strangled in the 

 salmon nets.* 



As the thresher is most in evidence on our coasts during the 

 summer inshoring of the pilchards and mackerel, it may safely 

 be assumed that those migratory and gregarious fishes form 

 the bulk of its food, at any rate in our seas. The thresher 

 may often be seen thrashing the surface of Cornish bays and 

 beating up the frightened pilchards. It is quite easy to watch 

 the flurried movements of its victims from the clifi^s, for they 

 colour the water a deep red wherever they are massed in 

 numbers. At intervals the thresher leaps what looks fully 

 its own length in the air, the bright sun making burnished 

 silver of its body and long tail, and descends in the thick 

 of the shoal. Some miles further out, and seen only from 

 boats, the great rorqual also hunts the pilchards, though in a 

 different manner, for the cetacean has no long and powerful 

 tail to help it. Therefore it swims round and round the 

 huddled pilchards, and then, when they are sufficiently gathered 

 in a small area, dashes open-mouthed through their midst with 

 a roar that makes itself heard a mile away. 



Like the adder, the thresher shark has been credited with 

 swallowing her young in order to preserve them from danger. 

 We have a somewhat analogous, but proven, case in one 

 of the pipe-fishes, in which the young have been seen in the 

 aquarium to take refuge in the father's pouch in which they 

 were hatched out. Science demands an open mind in the case 

 of both the thresher and adder, and science should have it, but 

 * Ann. Scot. Nat. Hist., January, 1900, p. 17. 



