FEATHERS. 15 



climb best, two toes are directed forward and two backwards ; 

 and in those that wade in rivers, marshes, &c., in search of fishes 

 or worms, the tarsi are so long that the animal seems to be 

 mounted on stilts. In all these animals there is a peculiar mech- 

 anism, by means of which, when they are perched upon a branch, 

 the weight of the body tends to flex their toes, and consequently 

 to make them closely embrace the object in their grasp ; an 

 arrangement which permits them to repose in the standing posi- 

 tion without any risk of falling while asleep. 



15. The feathers with which the body of birds is covered, 

 serve to protect them against cold and damp ; and they are also 

 powerful means of locomotion. They are composed of a horny 

 stalk, hollow at the base, and armed with beards, which them- 

 selves, have still smaller beards upon them : they are formed by 

 secreting organs which are analogous in their nature to those 

 which produce the hairs in mammalia. [The secreting organ 

 destined to form a feather is called a capsule, and often acquires 

 considerable length. According to the observations of M. F. 

 Cuvier, it would appear that the capsule grows during the whole 

 period occupied in the developement of the feather, and that in 

 proportion as its base elongates, its extremity dies and becomes 

 dry, the moment it has formed the corresponding portion of this 

 appendix. Each one of these little apparatuses is composed of 

 a cylindrical sheath, lined internally by two coats or tunics, united 

 by oblique partitions, and a central bulb. The substance of the 

 feather is deposited on the bulb, and to form the beards, it is 

 moulded in some way, in the spaces that the little partitions, we 

 have just mentioned, leave between them ; in the portion corres- 

 ponding to the stalk, the bulb is in relation with the internal surface 

 of the stalk, and after having there deposited a spongy substance 

 it dries and perishes : but at the part where the stalk or trunk of 

 the feather is tubular, the lamina of horny matter which this secre- 

 ting organ deposites, is shaped or moulded around itself and is 

 completely enveloped in it; nevertheless, the bulb, after it has 

 discharged its functions, dries, and forms, in perishing, a series of 

 membranous cones, lodged one in the other like a nest of boxes, 

 which fill the interior of the tube, and are called the soul of the 

 feather, or quill. 



lo". The new feather is at first enclosed in the sheath of its 

 capsule which frequently projects several inches beyond the skin, 

 and is gradually destroyed ; the feather then appears naked, and 

 its beards display themselves laterally; the extremity of its 



15. What are the uses of the feathers ? How are they formed ? 



16. Do birds shed their feathers ? 



2 



