Beginners' zoology . er, and Noble Pheasants, males. Order?(Key, p. 177.) Ornaments of males, brightest in season of courtship, are due tosexual selection (Figs. 321-7-9, 333). seen evidence of the moulting of birds? Describe themoulting process (page 120). BIRDS 175 Adaptations forFlying. — Flightis the most diffi-cult and energy-consuming meth-od of movingfound among ani-mals, and care-ful adjustment isnecessary. Forbalancing, theheaviest musclesare placed at thelower and centralportion of the are the flyingmuscles, and in somebirds (humming birds)they make half of theentire weigh
Beginners' zoology . er, and Noble Pheasants, males. Order?(Key, p. 177.) Ornaments of males, brightest in season of courtship, are due tosexual selection (Figs. 321-7-9, 333). seen evidence of the moulting of birds? Describe themoulting process (page 120). BIRDS 175 Adaptations forFlying. — Flightis the most diffi-cult and energy-consuming meth-od of movingfound among ani-mals, and care-ful adjustment isnecessary. Forbalancing, theheaviest musclesare placed at thelower and centralportion of the are the flyingmuscles, and in somebirds (humming birds)they make half of theentire weight. Teethare the densest of ani-mal structures; teethand the strong chew-ing muscles requiredwould make the headheavy and balancingdifficult; hence the chewing apparatus istransferred to the heavy gizzard near thecentre of gravity of the body. The birdsneck is long and excels all other necks inflexibility, but it is very slender (althoughapparently heavy), being inclosed in aloose, feathered skin. A cone is the best. 176 BEGINNERS ZOOLOGY shape to enable the body to penetrate the air, and a smallneck would destroy the conical form. The internal organsare compactly arranged and rest in the cavity of the breastbone. The bellows-like air sacs filled with warm airlighten the birds weight. The bones are hollow and verythin. The large tail quills are used by the bird only inguiding its flight up and down, or balancing on a limb. The feet also aid aflying bird m bal-ancing. The wingis so constructed asto present to theair a remarkablylarge surface com-pared with thesmall bony supportin the wing skele-ton. Are tubesever resorted to byhuman architects when lightness combined with strengthis desired } Which quills in the wing serve to lengthenit .^ (Fig. 296.) To broaden Is flight more difficultfor a bird or for a butterfly? Which of them do the flyingmachines more closely Can any bird fly for along time without flapping its wings }
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1921
