NATURAL THEOLOGY. 229 



much more exposed to the cold than large ones, 

 forasmuch as they present, in proportion to their 

 bulk, a much larger surface to the air. If a tur- 

 key were divided into a number of wrens, (sup- 

 posing the shape of the turkey and the wren to 

 be similar,) the surface of all the wrens would 

 exceed the surface of the turkey in the proportion 

 of the length, breadth, (or of any homologous line) 

 of a turkey to that of a wren, which would be, 

 perhaps, a proportion of ten to one. It was ne- 

 cessary, therefore, that small birds should be more 

 warmly clad than large ones ; and this seems to 

 be the expedient by which that exigency is pro- 

 vided for. 



II. In comparing different animals, I know no 

 part of their structure which exhibits greater va- 

 riety, or, in that variety, a nicer accommodation 

 to their respective conveniency than that which 

 is seen in the different formations of their mouths^ 

 Whether the purpose be the reception of aliment 

 merely, or the catching of prey, the picking up of 

 seeds, the cropping of herbage, the extraction of 

 juices, the suction of liquids, the breaking and 

 grinding of food, the taste of that food, together 

 with the respiration of air, and, in conjunction 

 with it, the utterance of sound ; these various 

 offices are assigned to this one part, and, in dif- 

 ferent species, provided for as they are wanted by 

 its different constitution. In the human species, 

 forasmuch as there are hands to convey the food 

 to the mouth, the mouth is flat, and by reason of 



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