. The structure and life of birds . a strong elastic liga-ment attached to the upright spines of the bird, as I shall show in the article on PassiveMachinery in the next chapter, has several whichare remarkable for their elasticity, some, if not all, ofthese having been originally tendons. Feathers—Structure and Development. A feather is a very elaborate appendage. Whenwe are told that a Peacocks or an Ostrichs plume, orthe wing-feather of an Albatross is an epidermicgrowth, part, that is, of the horny outer skin, weseem to hear words that explain nothing. There isanother epiderm
. The structure and life of birds . a strong elastic liga-ment attached to the upright spines of the bird, as I shall show in the article on PassiveMachinery in the next chapter, has several whichare remarkable for their elasticity, some, if not all, ofthese having been originally tendons. Feathers—Structure and Development. A feather is a very elaborate appendage. Whenwe are told that a Peacocks or an Ostrichs plume, orthe wing-feather of an Albatross is an epidermicgrowth, part, that is, of the horny outer skin, weseem to hear words that explain nothing. There isanother epidermic growth, the nature of which it isperhaps hardly less difficult to realise—the horn of a VI FORM AND FUNCTION 45 rhinoceros. But even with feathers, if we begin withthe simplest instead of the most elaborate, the diffi-culty will appear much less, though it may not entirelyvanish. A still better plan will be to begin with thescale of a reptile, and show how it corresponds to abirds feather. The scale proper is formed from the. Fig. 37. (n) Feather of Duck, carrying nestling down feather ; (/>) Nestling down of Thrush; (c) of Pigeon ; (d) Thread feather of Goose ; (7>), (c), and (it) after Gadow ; f, Feather proper ; N, Nestling down. skin, its horny coating from the epidermis. Where afeather is to grow, there is a little skin papilla orpimple, which corresponds to the scale proper ; theactual feather is formed from the epidermis thatcovers the papilla, and corresponds to the hornycovering of the scale. On the wings of the Penguin,or on the legs of birds of the Ostrich kind—, the L 146 THE STRUCTURE AND LIFE OF BIRDS CHAP. Rhea—may be found primitive feathers that are notvery different from the scales on the birds own legsor on a lizard. Birds in general have down feathersamong the large ones, and these down feathers areoften merely a little fluff at the top of a quill, thoughsometimes they are almost perfect miniatures of atypical feather. Besides these ther
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