420 FISHES. 



twenty years. The Suez Canal has already admitted two 

 new sharks to European waters, though they have not as 

 yet been observed west of Gibraltar. 



i. THE SHARKS. 



These cartilaginous fishes have the body tapering, the 

 tail with the upper lobe the larger, the snout pointed or 

 shovel-shaped, breathing-spiracles on the head behind the 

 eyes, the mouth, usually crescentic, beneath the head. The 

 eyes have a movable, nictitating membrane. The teeth, the 

 formation of which differs from that in teleostean fishes in 

 a manner that need not be particularised here, lie in rows, 

 the hinder ready to take the place of those in front. The 

 skin within the mouth is rough like that without, which 

 lacks scales. The lateral gill -openings are usually five, 

 sometimes six or seven, in number. The eye has, in some, 

 a closing membrane not found in other fishes. By these 

 features, as well as by the presence of claspers at the vent, 

 and several internal peculiarities (as the absence of air- 

 bladder, a spiral valve in the intestine, and the nature of 

 the optic nerves, which last are not transverse or decus- 

 sate, as in bony fishes), sharks are not difficult to distin- 

 guish. They are all of carnivorous tastes, though several, 

 as our Basking Shark and the Port Jackson Shark, are 

 quite inoffensive. In reproduction, they are mostly ovi- 

 parous, many depositing their eggs in oblong receptacles 

 of a horny substance, known as "purses." The hammer- 

 head, the porbeagle, the tope, and the smooth hound bring 

 forth their young alive. 



One of the handsomest of British sharks, the Blue ShaFk, 



is plentiful on the Cornish coast every summer, where nets 



Blue are ruined and long lines torn to shreds. I 



Shark, have hooked small examples of 20 or 30 Ibs. on 



the rod, but sharks of this species have been taken in the 



nets of twice the weight and at least 6 feet in length. 



