160 NATURAL THEOLOGY. 



structure of the feet of birds, in their original form, was 

 critically adapted to their original destination I The web- 

 feet of amphibious quadrupeds, seals, otters, etc., fall under 

 the same observation. 



IX. The Jive senses are common to most large ani- 

 mals ; nor have we much difference to remark in theii 

 constitution, or much, however, which is referable to mech- 

 anism. 



The superior sagacity of animals which hunt their prey, 

 and which, consequently, depend for their livelihood upon 

 their nose, is well known in its use ; but not at all known in 

 the organization which produces it. 



The external ears of beasts of prey, of lions, tigers, 

 wolves, have their trumpet-part, or concavity, standing for- 

 ward, to seize the sounds which are before them, namely, 

 the sounds of the animals which they pursue or watch. 

 The ears of animals of flight are turned backward, to give 

 notice of the approach of their enemy from behind, whence 

 he may steal upon them unseen. This is a critical dis- 

 tinction, and is mechanical ; but it may be suggested, and 1 

 think not without probability, that it is the effect of contin- 

 ual habit. 



The eyes of animals which follow their prey by nighS 

 as cats, owls, etc., possess a faculty not given to those ol 

 other species, namely, of closing the pupil entirely. The 

 final cause of which seems to be this : it was necessary for 

 Buch animals to be able to descry objects Mdth very small 

 degrees of light. This capacity depended upon the superior 

 sensibility of the retina ; that is, upon its being affected by 

 the most feeble impulses. But that tenderness of structure 

 which rendered the membrane thus exquisitely sensible, ren- 

 dered it also liable to be offended by the access of stronger 

 degrees of light, The contractile range, therefore, of the 

 pupil is increased in these animals, so as to enable them to 

 close the aperture entirely, which includes the power of 

 diminishing it in every degree ; Vv^hereby at all times such 



