OF THE GANNET. 293 



the air in those cells breaks its fall ; acts like a para- 

 chute in preventing it from going too deep ; probably 

 invigorates its vital system by the application of a 

 portion of air, condensed by the resistance and cool- 

 ing effect of the water, to the coats of the arteries ; 

 and, what is more to our present purpose, assists it in 

 recovering its position, in order that it may remount 

 the sky, after it has either caught its prey or failed in 

 doing so. This quantity of air is of course condensed 

 by the collision ; but when that is over it expands 

 and raises the anterior part of the body, and at the 

 same time throws the centre of gravity further back- 

 wards, or more in a line with the feet. These at the 

 same time press downward with their curious webs, 

 both brought under the body by the position in which 

 the toes are articulated on the tarsi, and so heave the 

 body upward in the same manner, or at least upon 

 the same principle, that ordinary swimming feet impel 

 the body of a bird forward. Thus, what with the 

 action of the air, and what with that of the feet, the bird 

 is able to regain the wing without any difficulty. 



When the proper action of the foot is connected 

 with some action of the wings of the bird, as adapting 

 the foot for some particular kind of surface, or to 

 accomplish some other object in the general economy 

 of the creature, it always lessens the perfection 

 of the organ as a foot, whether for swimming or for 

 walking. 



Concentration upon one single part, or upon the 

 smallest number of parts possible, is always the 

 structure of maximum action in nature. We find 

 it in the wing of the swift, in the foot of the ostrich, 

 in the feet of all the swifter running birds, and in the 

 more perfect swimmers ; for though these have the 

 back toe with a marginal lobe, which appears to 



