i62 COMPENSATION. 



V. The spifler^s irch is a compensating contrivance 

 The spider lives upon flies, without wings to pursue them ; 

 a case, one would have thought, of great difficulty : yet 

 provided for; and provided for by a resource, which no 

 stratagem, no effort of the animal, could have produced, 

 had not both its external an internal structure been speci- 

 fically adapted to the operation. 



VI. In many species of insects the eye is fixed ; and 

 consequently without the power of turning the pupil to the 

 object. This great defect is however perfectly compensate 

 cd; and by a mechanism which we should not suspect. 

 The eye is a multiplying glass ; with a lens looking in 

 every direction, and catching every object. By which 

 means, although the orb of the eye be stationary, the field 

 of vision is as ample as that of other animals ; and is 

 commanded on every side. (PI. XXX. fig. 8.) When 

 this lattice work was first observed, the multiplicity and 

 minuteness of the surfaces must have added to the surprise 

 of the discovery. Adams tells us, that fourteen hundred 

 of these reticulations have been counted in the two eyes of 

 a drone bee. 



In other cases, the compensation is effected by the num- 

 ])er and position of the eyes themselves. (Pi. XXX. fig. 9.) 

 The spider has eight eyes, mounted upon different parts of 

 the head, two in front, two in the top of the head, two on 

 each side. These eyes are without motion ; but, by their 

 situation, suited to comprehend every view, which the wants 

 or safety of the animal render it necessary for it to take. 



VII. The memoirs for the Natural History of Animals, 

 published by the French Academy, A. D. 1687, furnish us 

 with some curious particulars in the eye of a chamelion. 

 Instead of two eyelids, it is covered by an eyelid with a 

 hole in it. This singular structure appears to be ?i cofnpen- 

 satorij, and to answer to some other singularities in the 

 shape of the animal. The neck of the chamelion is inflex- 

 ible. To make up for this, the eye is so prominent, as that 

 more than half of the ball stands out of the head. By 

 means of which extraordinary projection, the pupil of the 

 eye can be carried by the muscles in every direction, and 

 is capable of being pointed towards every object. But, 

 then, so unusual an exposure of the globe of the eye, re- 

 quires, for its lubricity and defence, a more than ordinary 

 protection of eyelid, as well as a more than ordinary supply 

 of moisture ; yet the motion of an eyelid, formed accord- 

 ing to the common construction, would be impeded, as it 



