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The largest seal, at left end of group, is the

FIG. 71.-A fur seal (Callorhinus alascanus) family on the Vostochni rookery, St. Paul Island. male.-Photograph by D. W. THOMPSON and A. W. MARRETT.

of his bright feathers. The female consents to be chosen by the one which pleases her. It is believed that the handsomest, most vivacious, and most musical males are the ones most successful in such courtship. With polygamous animals there is intense rivalry among the males in the mating season, which in almost all species is in the spring. The strongest males survive and reproduce their strength. The most notable adaptation is seen in the superior size of teeth, horns, mane, or spurs. Among the polygamous fur seals (Fig. 71) and sea lions the male is about four times

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FIG. 72.-A wild duck (Aythya) family. Male, female, and præcocial young.

the size of the female. In the polygamous family of deer, buffalo, and the domestic cattle and sheep, the male is larger and more powerfully armed than the female. In the polygamous group to which the hen, turkey, and peacock belong the males possess the display of plumage, and the structures adapted for fighting, with the will to use them.

79. Adaptations for the defense of the young. The protection of the young is the source of many adaptive structures as well as of the instincts by which such structures are

utilized. In general, those animals are highest in development, with best means of holding their own in the struggle

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FIG. 73.-The altricial nestlings of the Blue jay (Cyanocitta cristata). for life, that take best care of their young. The homes of animals are elsewhere specially discussed (see Chapter

XV), but those instincts which lead to home-building may all be regarded as useful adaptations in preserving the young. Among the lower or more coarsely organized

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FIG. 74.-Kangaroo (Macropus rufus) with young in pouch.

birds, such as the chicken, the duck, and the auk, as with the reptiles, the young animal is hatched with well-developed muscular system and sense

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FIG. 75.-Egg-case of California barn-door skate (Raja binocu

organs, and is capable of running
about, and, to some extent, of feed-
ing itself. Birds of this type are
known as præcocial (Fig. 72), while
the name altricial (Fig. 73) is ap-
plied to the more highly organized
forms, such as the thrushes, doves,
and song-birds generally. With
these the young are hatched in a
wholly helpless condition, with in-
effective muscles, deficient senses,
and dependent wholly upon the
parent. The altricial condition de-
mands the building of a nest, the
establishment of a home, and the
continued care of one or both of

lata) cut open to show young the parents.
inside. (Young issues natu-
rally at one end of the case.)

The very lowest mammals known,
the duckbills (Monotremes) of
Australia, lay large eggs in a strong shell like those of a
turtle, and guard them with great jealousy. But with
almost all mammals the egg is very small and without
much food-yolk. The egg begins its development within
the body. It is nourished by the
blood of the mother, and after birth
the young is cherished by her, and
fed by milk secreted by specialized
glands of the skin. All these features
are adaptations tending toward the
preservation of the young. In the
division of mammals next lowest to the Monotremes-the
kangaroo, opossum, etc.-the young are born in a very im-
mature state and are at once seized by the mother and

FIG. 76.-Egg-case of the cock-
roach.

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