620 CYPSELUS MURARIUS. 



gliding or quick evolution. For the latter the surface of the 

 wing must be extended in length and narrowed, and instead 

 of presenting a concavity must be straight in the horizontal 

 direction. Accordingly in the Swift the wing has its humeral 

 articulation peculiarly free, insomuch that holding one alive 

 in your hand you at first imagine that its wings have been 

 broken. At the same time, their muscular apparatus is remark- 

 ably strong. Then the secondary quills are very short, and 

 the primaries gradually and rapidly elongated, and furnished 

 with very strong but highly elastic shafts. The tail, although 

 not so long, is similarly constructed, being deeply forked, and 

 so in a manner divided into two pointed and elongated laminse 

 similar in some degree to the wings, and aiding their action 

 in executing turns. In seizing its prey, while gliding or flut- 

 tering in the air, the bird would be incommoded by any length 

 of neck; that part is therefore extremely abbreviated, so that 

 the head seems as if stuck upon the shoulders, as is the case, 

 for a similar reason, in the Cetacea and fishes. A long pointed 

 bill would be of use only to a bird that has objects to pick from 

 the ground or any other surface, or from among soil or foliage. In 

 the present case, the bird, carried with rapidity to its tiny prey, 

 merely requires to open its mouth, which is extremely en- 

 larged, and supplied with an abundant viscid secretion, which 

 immediately entangles the fly that has been caught, and pre- 

 vents its escape should the mouth be opened the next instant. 

 A bird so living has no need of walking, and there being 

 nothing superfluous in nature, its feet are reduced to cramping 

 organs, by which it can cling to any kind of surface when en- 

 tering its nest, and its gait is merely a hobbling motion, aided 

 by the wings. It cannot rise from a flat surface, as I have as- 

 certained by experiment, but it launches from any little emi- 

 nence, and if it can spring out horizontally, is enabled to fly oft', 

 although its usual mode of launching is like that of the Gannet 

 by a deep curve. 



These two birds are very similar in some points of their 

 organization. Their wings are long and narrow, and their 

 flight is rapid and buoyant ; they seize their prey by throwing 

 themselves with velocity upon it ; they launch from the rocks 



