254 NATURAL THEOLOGY. 



II. The oil with which birds preen their fea- 

 thers, and the organ which supplies it, is a specific 

 provision for the winged creation. On each side 

 of the rump of birds is observed a small nipple, 

 yielding upon pressure a butter-like substance, 

 which the bird extracts by pinching the pap with 

 its bill. With this oil or ointment, thus procured, 

 the bird dresses his coat; and repeats the action 

 as often as its own sensations teach it that it is in 

 any part wanted, or as the excretion may be suf- 

 ficient for the expense. The gland, the pap, the 

 nature and quality of the excreted substance, the 

 manner of obtaining it from its lodgement in the 

 body, the application of it when obtained, form, 

 collectively, an evidence of intention which it is not 

 easy to withstand. Nothing similar to it is found 

 in unfeathered animals. What blind conatus of 

 nature should produce it in birds ; should not pro- 

 duce it in beasts ? 



III. The air-bladder also of a fish affords a 

 plain and direct instance, not only of contrivance, 

 but strictly of that species of contrivance which 

 we denominate mechanical. It is a philosophical 



head, to that which, like the spring of a steelyard, weighs against 

 the immense head of the elephant. 



These elastic ligaments vary witli the length and motion of the 

 neck. It would be tedious to describe their varieties in tlie camel, 

 cameleopard, ostrich, &c. We may be satisfied with the fact, that 

 the elastic hgament is a structure extensively used in the animal 

 textures, generally coming in aid of the muscles, or as a substi- 

 tute for them. 



