242 



INTRODUCTION TO ZOOLOGY. 



the deck, is to chop off its tail, as danger is to he apprehended 

 from the great strength with which it is used. Captain Basil 

 Hall gives a most animated and seamanlike description of the 

 entire scene.* 



Some of the Sharks attain a great size. The Basking Shark, 

 a species found off these coasts, has heen known to measure 

 thirty-six feet in length, and is one of the largest of the true 

 fishes, t The Blue Shark has been celebrated for its affection 

 for its young; and the belief yet prevails that the young are 

 accustomed to seek safety from danger by entering the mouth 

 of the parent fish, and taking shelter in its belly. That they 

 have been found alive in the stomach is admitted; but that 

 they went there voluntarily, or for safety, seenis more than 

 doubtful.J 



A beautiful example of beneficent design is afforded by a 

 peculiarity of structure observable in the young of Sharks and 

 Skates, whilst still imprisoned in the egg-case. From the gills 

 there are projecting filaments; each of these contains a minute 

 blood-vessel, and serves thus to expose the blood to the 

 purifying action of the water within the horny egg-case. 

 These appendages, like those of the Tadpole hereafter men- 

 tioned, are only temporary; but 

 they fulfil, at an early period of 

 growth, the function which is after- 

 wards so efficiently performed by 

 the gills. 



A more striking example of pro- 

 vidential care is perhaps afforded 

 by the arrangement which furnishes 

 to the Sharks the means of keeping 

 their formidable array of teeth (Fig. 

 197) fit to execute at all times their 

 fearful office. They must be liable 

 to be displaced and broken, and if 

 fixed in sockets, as our teeth are, 

 and no means provided for a suc- 

 cessive series, it is obvious that 

 these formidable monsters of the 

 deep would in time perish, from ina- 

 bility to seize their prey. But this 



Fig. 197. HEAD OF SHARK. 



Fragments of Voyages and Travels. Second Series, vol. i. p. 267. 

 t Yarrell, p, 39G. f Tarrell, p. 381. 



