308 



THE REASON WHY : 



More certain was the crowing of the cock 



To number hours, than is the abbey clock ; 



And sooner than the matin bell was rung, 



He clapp d his wings upon his roost and sung.&quot; DKYDEN. 



the centre of gravity is thrown a little behind the centre of articulation of the wings, 

 &amp;lt;tnd therefore nearer the centre of the base of sustentation by the backward position 

 1 2 



of the head. In the case of birds, such, for example, as the penguin, fig. 2, having 

 a short and neai-ly inflexible neck and legs, which are incapable of being advanced, 

 the animal, when it stands, is obliged to assume the vertical position.* 



984. Why do many birds roost upon one leg ? 



Because the heavier the body presses upon the bent joint, from 

 the peculiar construction of the foot, the tighter the claws are 

 pulled round the branch or perch ; and it follows that the weight 

 of ihe bird must pull more when it falls upon one set of muscles, 

 than when it is divided between the two sets ; a firmer and 

 steadier position is by this means achieved. 



985. Why does the formation of the beak of birds indicate 

 the substances they feed upon ? 



Because nature has adapted the instrument to its employment 

 with such nicety that the forms of the beak are as various as the 

 qualities of the substances used as food ; and so close and 

 invariable is this relation between the mechanical structure of 

 the instrument of prehension and the aliment, that a praclical 



Larclner s &quot; Animal Physics. 



