COMPENSATION. 161 



compensate for the decrepitude of its legs and feet. With- 

 out her hook, the bat would be the most helpless of all 

 animals. She can neither run upon her feet, nor raise 

 herself from the ground. These inabilities are made up 

 to her by the contrivance in her wing ; and in placing 

 a claw on that part, the Creator has deviated from the 

 analogy observed in winged animals. A singular defect 

 required a singular substitute. 



III. The crane kind are to live and seek their food 

 amongst the waters ; yet, having no web-feet, are incapa- 

 ble of swimming. To make up for this deficiency, they 

 are furnished with long legs for wading, or long bills for 

 grouping ; or usually with both. This is compensation. 

 But I think the true reflection upon the present instance 

 is, how every part of nature is tenanted by appropriate in- 

 habitants. Not only is the surface of deep waters peopled 

 by numerous tribes of birds that swim, but marshes and 

 shallow pools are furnished with hardly less numerous tribes 

 of birds that wade. 



IV. The common parrot has, in the structure of its 

 beak, both an inconveniency, and a compensation for it. 

 When I speak of an inconveniency, I have a view to a di- 

 lemma which frequently occurs in the works of nature, viz. 

 that the peculiarity of structure by which an organ is made 

 to answer one purpose, necessarily unfits it for some other 

 purpose. This is the case before us. The upper bill of a 

 parrot is so much hooked, and so much overlaps the lower, 

 that, if, as in other birds, the lower chap alone had motion, 

 the bird could scarcely gape wide enough to receive its 

 food ; yet this hook and overlapping of the bill could not 

 be spared, for it forms the very instrument by which the 

 bird climbs ; to say nothing of the use which it makes of 

 it in breaking nuts, and the hard substances upon which it 

 feeds. How, therefore, has nature provided for the open- 

 ing of this occluded mouth ? By making the upper chap 

 moveable, (PI. XXX. fig. 7.) as well as the lower. In 

 most birds, the upper chap is connected, and makes but 

 one piece with the skull ; but in the parrot, the upper chap 

 is joined to the bone of the head by a strong membrane, 

 placed on each side of it, which lifts and depresses it at 

 pleasure. * 



* Goldsmith's Nat. Hist. vol. v. p. 274. 

 P 



