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females, and for the control of his harem others are ready at all
times to dispute the possession. But with monogamous animals
like the true or hair seal or fox, where a male mates with a single
female, there is no such discrepancy in size and strength, and
the warlike force of the male is spent on outside enemies, not
on his own species.
The movements of many migratory animals are mainly con-
trolled by the impulse to reproduce. Some pelagic fishes, es-
pecially flying fishes and fishes allied to the mackerel, swim
long distances to a region favorable for a disposition of spawn.
Some species are known only in the waters they make their
breeding homes, the individuals being scattered through the
wide seas at other times. Many fresh-water fishes, as trout,
suckers, etc., forsake the large streams in the spring, ascending
the small brooks where they can rear their young in greater
safety. Still others, known as anadromous fishes, feed and
mature in the sea, but ascend the rivers as the impulse of re-
production grows strong. Among such species are the salmon,
shad, alewife, sturgeon, and striped bass in American waters.
The most noteworthy case of the anadromous instinct is found
in the king salmon or quinnat of the Pacific coast. This great
fish spawns in November. In the Columbia River it begins
running in March and April, spending the whole summer in
the ascent of the river without feeding. By autumn the in-
dividuals are greatly changed in appearance, discolored, worn,
and distorted. On reaching the spawning beds, some of them
a thousand miles from the sea, the female deposits her eggs in
the gravel of some shallow brook. After they are fertilized
both male and female drift tail foremost and helpless down the
stream, none of them ever surviving to reach the sea. The same
habits are found in other species of salmon of the Pacific, but
in most cases the individuals of other species do not start so
early or run so far. A few species of fishes, as the eel, reverse
this order, feeding in the rivers and brackish creeks, dropping
down to the sea to spawn.
The migration of birds has relation to reproduction as well
as to changes of weather. As soon as they reach their summer
homes, courtship, mating, nest-building, and the care of the
young occupy the attention of every species.
In the animal kingdom one of the great factors in develop-
ment has been the care of the young. This feature is a prominent


one in the specialization of birds and mammals. When the young are cared for the percentage of loss in the struggle for life is greatly reduced, the number of births necessary to the


Fig. 274.—Nest and eggs of the Rufus hummingbird, Trochilus rufus. (Photograph by

J. 0. Snyder. Stanford University, California.)

maintenance of the species is much less, and the opportunities for specialization in other relations of life are much greater. In these regards, the nest-building and home-making animals have the advantage over those that have not these instincts. The animals that mate for life have the advantage over polyg. amous animals, and those whose social or mating habits give


Tarla Beads Fig. 275.- Altricial nestlings of the blue jay, Cyanocitta cristata.

rise to a division of labor over those with instincts less highly specialized.

When we study instincts of animals with care and in detail, we find that their regularity is much less than has been supposed. There is as much variation in regard to instinct among individuals as there is with regard to other characters of the species. Some power of choice is found in almost every operation of instinct. Even the most machinelike instinct shows some degree of adaptability to new conditions. On the other hand, in no animal does reason show entire freedom from automatism or reflex action. “The fundamental identity of instinct with intelligence,” says an able investigator, “is shown in their dependence upon the same structural mechanism (the brain and nerves), and in their responsive adaptability.”


Fig. 276.-A wild duck, A ythyo, family; male, female, and præcocial young.

Reason or intellect, as distinguished from instinct, is the choice, more or less conscious, among responses to external impressions. Its basis, like that of instinct, is in reflex action. Its operations, often repeated, become similarly reflex by repetition, and are known as habit. A habit is a voluntary action repeated until it becomes reflex. It is essentially like instinct in all its manifestations. The only evident difference is in its origin. Instinct is inherited. Habit is the reaction produced within the individual by its own repeated actions. In the varied relations of life the pure reflex action becomes inadequate. The sensorium is offered a choice of responses. To choose one and to reject the others is the function of intellect or reason. While its excessive development in man obscures its close relation to instinct, both shade off by degrees into reflex

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