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 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 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 binocu organs, and is capable of running lata) cut open to show young the parents. The very lowest mammals known, FIG. 76.-Egg-case of the cock- |