90 SALT-WATER FISHES 



it cannot be claimed that the testimony is particularly strong 

 in either case. There is just this much of evidence, though 

 very indirect, in the case of the shark, which does not equally 

 apply to the reptile, and that is that the young sharks would 

 not, like the young adders, be safer if allowed to scatter on 

 their own account. Other fishes, stronger swimmers than 

 they, would certainly capture them without difficulty, whereas 

 it is not easy to imagine any natural enemy of young adders 

 that would be able to catch them if they were allowed to 

 disperse quickly and unobtrusively in the grass. In their 

 parent, on the other hand, one blow would dispose of the 

 whole brood. 



The very circumstantial accounts of the thresher shark 

 leaping out of water, and striking sounding blows on the 

 backs of whales have been disbelieved in many quarters, 

 chiefly owing to the pretensions of some naturalists, who know 

 these creatures only in the dissecting-room, to find in the 

 shape and size of the thresher's teeth the whole explanation 

 of its mode of life. On the other hand, most who have 

 travelled in the southern ocean can recall at some time or 

 other a vivid picture of one or more threshers leaping on 

 some unfortunate whale. As it happens, too, the laboratory 

 disbeliever is often encouraged in his want of faith by the 

 fatal tendency on the part of travellers to embellish their 

 accounts with additions of their own. In the present instance 

 this already unequal duel has been complicated by the intro- 

 duction of a sword-fish, an ally in this case of the sharks, 

 which is said to keep the unfortunate whale at the surface by 

 prodding it with its snout. Now, it is quite true that if there 

 be not some such deterrent as a sword-fish in attendance, it is 

 singular that the instinct of the whale should not warn it to 

 sink under water, where the blows from the thresher's tail 

 would be comparatively harmless. At the same time, for all 

 we know to the contrary, its instinct may be at fault, and, as 

 the weapon of the sword-fish has not yet been seen in the fray, 



