512 THE MKCHAMCAL FUNCTIONS. 



quill, which is prolonged for the purpose of con- 

 verting it into a lever of sufficient length for the 

 mechanical office it has to perform. In proportion 

 as each structure is tinished, she neglects not to 

 remove the scaffi)ldings which had been set up as 

 temporary structures ; the membranes, with all their 

 partitions, are carried away, the vascular pulp of 

 the bulb is absorbed, and its place supplied by 

 air, thus securing the utmost lightness, without 

 any diminution of strength. Is it possible for any 

 rational mind, after meditating upon these facts, 

 to arrive at the persuasion that they are all the 

 mere results of chance ? 



Several circumstances remain to be noticed res- 

 pecting the structure and actions of the wings of 

 birds. If we attend to the mode of their articula- 

 tion with the scapula, we find it producing a motion 

 oblique with regard to the axis of the body, so that 

 the stroke which they give to the air is directed 

 both downwards and backwards ; and the bird, 

 while moving forwards, is at the same time sup- 

 ported in opposition to the force of gravity. The 

 different portions of the wing are likewise so dis- 

 posed as to be contracted and folded together when 

 the wing is draM^i up, but fully expanded when it 

 descends in order to strike the air. It is obvious 

 that, without this provision, a great part of the 

 motion acquired by the resistance of the air against 

 the wing in its descent would have been lost by a 

 counteracting resistance during its ascent. The 

 disposition of the great feathers is such that they 

 strike the air with their flat sides, but present only 

 their edges in rising : what is called feathering the 



