. Bird-lore . e, ii is a dead structure, physiologically disconnected from thebody and serving only in a mechanical way for flight and protection. To under- The Audubon Societies 305 stand what actually happens in the case of these birds, it is necessary to knowsomething of the structure of the feather as shown under the lens. All feathers are composed of a mid-vein or shaft and the web. If the webis examined carefully it will be seen to be composed of a series of fibers calledbarbs attached on each side of the shaft. Each barb, similarly, bears tworows of barbules. When the barbules are exami
. Bird-lore . e, ii is a dead structure, physiologically disconnected from thebody and serving only in a mechanical way for flight and protection. To under- The Audubon Societies 305 stand what actually happens in the case of these birds, it is necessary to knowsomething of the structure of the feather as shown under the lens. All feathers are composed of a mid-vein or shaft and the web. If the webis examined carefully it will be seen to be composed of a series of fibers calledbarbs attached on each side of the shaft. Each barb, similarly, bears tworows of barbules. When the barbules are examined under the microscope,they are found to bear a number of minute recurved hooklets which fasteninto the hooklets of adjacent barbules and give to the feather its firmness,being best developed in the flight feathers, which require the greatest feathers, and the innermost parts of most feathers, lack this device andare, therefore, always soft and fluffy, giving little resistance to the passage of. MALE HOUSE SPARROWS IN SUMMER AND IN WINTER PLUMAGE Note that in winter the black throat and breast is nearly concealed by the gray tips of the feathers. In the spring they wear off, revealing the black beneath air through them. Now in the case of the Purple Finch and Indigo Bunting,the red and blue colors are located mostly in the barbs, while the barbules andhooklets are dusky. With the wearing away of the barbues and hooks on thebody feathers, the barbs become more conspicuous and the color of the birdbecomes apparently more intense. That molting is not confined to birds is well recognized and its homologyto the shedding of the skin in reptiles and amphibians is conceded. Of course,the snake or amphibian does not actually shed its skin but merely the hardouter cuticle. This cuticle, as in the case of the birds feathers when fullyformed, is a dead structure and it is inelastic. Consequently, as the snake orfrog or salamander grows, this shell becomes too small for it a
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