PROTECTION OF THE EYE. 313 



delicate as those of sound and light ; or enjoying 

 these, by instruments so exquisitely framed, how 

 are these instruments to be protected from the 

 ruder shocks to which they must be exposed ? 

 These considerations lead to the conclusion that 

 if he object to one part of the system, he objects 

 to the whole of that by which we hold our present 

 existence. 



The motions of the eye and eyelids, which are 

 directed by this sensibility, must be performed 

 with extreme rapidity. To rinse any thing in wa- 

 ter, or to rid it of dust by shaking it in the wind, 

 the action must be quick ; and such a motion is 

 possessed by the eye of the fish, although the eye- 

 lids and lachrymal apparatus are in them unne- 

 cessary. 



If we are giving proofs of design, we can have 

 none more obvious than that suggested in the Pre- 

 liminary Discourse, in the eye of the mud crab, 

 an animal which, like the eel, seeks its food in 

 mud and turbid water. Emerging from such a 

 bed, its eye is covered with slime, and would be 

 useless : but to provide against this inconvenience 

 there is a little brush near the eye, to which the 

 prominent horny eye can be raised, and against 

 which it is wiped, with an action as intelligible as 

 that of a man wiping his spectacles. The cray- 

 fish, too, which burrows in the banks of rivers, has 

 the same provision, although the structure is less 

 perfect. 



I have assumed that the action of the eye of 

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