BOOK OF NATURE LAID OPEN. 143 



with a slimy glutinous matter, supposed to be se- 

 creted from the pores of their bodies. A protube- 

 rant eye would have been inconvenient, and easily 

 injured by moving in such a dense medium ; but, to 

 prevent this, the eyes of fishes are sunk in their heads, 

 and the cornea made flat, while the defect of vision, 

 that must have inevitably ensued in consequence, had 

 they been formed like those of other animals, is pro- 

 vided against by the spherical form of the crystalline 

 humour. As their progression is performed in a 

 different way from that of any of the tribes we have 

 already noticed, they are provided with instruments 

 peculiar to themselves, and are enabled to poise their 

 bodies, and push swiftly along by means of their fins 

 and tail Not being provided with hands or feet to 

 lay hold of their prey, or with talons or bills to tear 

 it to pieces, Nature has provided them with mouths 

 capable of great extension, when they have occasion 

 to seize on their victims, yet so formed, that when 

 shut up close, they terminate in a point, in which an 

 opening is scarcely distinguishable. What a tre- 

 mendous chasm, for instance, does the mouth of a 

 Shark present when extended to receive a human 

 carcase, of which this voracious monster has given 

 instances of being extremely fond, and yet, when 

 closed, it appears but a continuation of that long snout 

 with which this fish, (reckoned among the swiftest of 

 swimmers) like an arrow pierces the watery element. 

 In the absence of necks, which would make the 

 head too apt to be turned aside when making their 

 way against a stream, the whole bodies of fish are 



