186 NATURAL THEOLOGY. 



part of nature is tenanted by appropriate inhabitants. Not 

 only is the surface of deep waters peopled by numerous tribes 

 of birds that swim, but marshes and shallow pools are fur- 

 nished with hardly less numerous tribes of birds that wade. 



IV. The common 2^0'f'i'ot has, in the structure of its beak, 

 both an inconveniency and a compe7isation for it. When 1 

 speak of an inconveniency, I have a view to a dilemma which 

 frequently occurs in the works of nature, namely, that the 

 peculiarity of structure by which an organ is made to an- 

 swer one purpose, necessarily unfits it for some other pur- 

 pose. This is the case before us. The upper bill of the 

 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 opening of this occlud- 

 ed mouth ? By making the upper chap movable, 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. =^ 



y. The spider's web is a compensating contrivance. 

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

 a case, one would have thought, of great difficulty, yet pro- 

 vided for, and provided for by a resource which no strata- 

 gem, no effort of the animal, could have produced, had not 

 both its external and internal structure been specificaUy 

 adapted to the operation. 



VI. In many species of insects the eye is fixed, and con- 

 sequently without the power of turning the pupil to the ob- 

 ject This great defect is, however, perfectly compensated^ 

 * Goldsmith's Nat. Hist., vol. 5, p. 274. 



