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

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 polyg amous 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

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

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

FIG. 75.-Egg-case of California barn-door skate (Raja binoculata) cut open to show young inside. (Young issues naturally at one end of the case.)

organs, and is capable of running about, and, to some extent, of feeding itself. Birds of this type are known as præcocial (Fig. 72), while the name altricial (Fig. 73) is applied 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 ineffective muscles, deficient senses, and dependent wholly upon the parent. The altricial condition dcmands the building of a nest, the establishment of a home, and the continued care of one or both of the parents.

The very lowest mammals known, the duck- bills (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 immature state and are at once seized by the mother and

FIG. 76.-Egg-case of the cockroach.