actions and reactions. Under the head of psychic functions are included all operations of the nervous system as well as all functions of like nature which may exist in organisms without specialized nerve fibers or nerve cells. As thus defined mind would include all phenomena of irritability, and even plants have the rudiments of it. The operations of the mind in this sense need not be conscious. With the lower animals almost all of them are automatic and unconscious. With man most of them must be so. All functions of the sensorium, irritability, reflex action, instinct, reason, volition, are alike in essential nature though differing greatly in their degree of specialization.

In another sense the term mind is applied only to conscious reasoning or conscious volition. In this sense it is mainly an attribute of man, the lower animals showing it in but slight degree. The discussion as to whether lower animals have minds turns on the definition of mind, and our answer to it depends on the definition we adopt.

FIG. 155.-A "pointer" dog in the act of "pointing," a specialized instinct.
(Permission of G. O. Shields, publisher of Recreation.)

CHAPTER XV

HOMES AND DOMESTIC HABITS

142. Importance of care of the young.-The nest-building and domestic habits of animals are adaptations, but adaptations of behavior or habit rather than of structure, and are based on instinct, intelligence, and reason. These instincts and habits are among the most important shown by animals, because on them depends largely the continuance of the species. Of primary importance in the perpetuation of the species is the possession by animals of adaptations of structure and behavior, which help the individual live long enough to attain full development and to leave offspring. But in the case of many animals a successful start in life on the part of the offspring depends on the existence in the parents of certain domestic habits concerned with the care and protection of their young. The young of many animals depend absolutely, for a part of their lifetime, on this parental care. In these cases it is quite as necessary for the continued existence of the species that the habits that afford this care be successful as that the parent should come successfully to mature development and to the production of offspring.

143. Care of the young, and communal life.-The nestbuilding or home-making habits and the continued personal care of the young for a part of their lifetime are most highly developed and widespread among the birds, mammals, and insects; and it is both among the insects and the higher vertebrates that we find most developed those social and communal habits discussed in Chapter IX. The principal activities of an animal community have to do

with the protection and sustenance of the young, and the care of the young is undoubtedly a chief factor in the development of communal life.

144. The invertebrates (except spiders and insects).Among the lower invertebrates parental aid to the young is confined almost exclusively to exhibitions of pure instinct. And this is true of many of the higher animals also. Eggs are deposited in sheltered places, and in such places and under such circumstances that the young on hatching will find themselves close to a supply of their natural food. The depositing of eggs in water by parents with terrestrial habits whose young are aquatic, is an example. The toad, which lives on land, feeding on insects, has young which live in water and feed on minute aquatic plants (alga). The dragon fly, that hawks over the pond or brook with glistening wings, has young that crawl in the slime and mud at the bottom of the pool. With most animals, after laying eggs, the parents show no further solicitude toward their offspring. The eggs are left to the vicissitudes of fortune, and the parents know nothing of their fate. In many cases the parent dies before the young are hatched. The mammals and birds are the only two great groups excepted, although there are numerous specific exceptions scattered among the lower invertebrates, fishes, batrachians, and higher invertebrates, notably the insects.

There are no instances of care of the

young after hatching among the sponges, polyps, worms, or star-fishes and sea-urchins, and but few among the crustaceans and mollusks. But there are in some of these groups a few cases of nest or home building in a crude and simple way. tain sea-urchins (Fig. 156) and worms and mollusks bore into stones, and remain in the shelter afforded by the cavity. A shell-fish (Lima hiams) cements together bits of coralline, shells, and sand to form a crude nest or hidingplace. The cray-fish digs a cylindrical burrow in the ground in which it can hide.

145. Spiders. Most spiders spin silken cocoons or sacs in which to deposit their eggs. Some spiders carry this egg-filled cocoon about with them for the sake of protecting the eggs. After hatching, the spiderlings remain in the cocoon a short time, feeding on each other! Thus only the

strongest survive and issue from the cocoon to earn their living in the outer world. With certain species of spiders the young after hatching leave the cocoon and gather on the back of the mother and are carried about by her for some time. In connection with their webs or snares many spiders have silken tunnels or tubes in which to lie hidden, a sort of sheltering nest. Those spiders that live on the ground make for themselves cylindrical burrows or holes in the ground, usually lined with silk, in which they hide when not hunting for food. Especially interesting among the many kinds of these spider nests are the burrows of the various trap-door spiders. These spiders are common in California and some other far Western States. The bur

row (Fig. 157) or cylindrical hole is closed above by a silken, thick, hinged lid or door, a little larger in diameter than the hole and neatly beveled on the edge, so as to fit tightly into and perfectly cover the hole when closed. The upper surface of the door is covered with soil, bits of leaves, and wood, so as to resemble very exactly the ground surface about it. We have found these trap-door nests in California in moss-covered ground, and here the lids of the nests were always covered with green, growing moss.

An English naturalist who studied the habits of these trap-door spiders found that if he removed the soil and bits of bark and twigs, or the moss, from the upper surface of the lid the spider always re-covered it. It is, of course, plain that by means of this covering the nest is perfectly concealed, the surface of the closed door not being different from the surrounding ground surface. This naturalist finally removed the moss not only from the surface of a trap-door, but also from all the ground in a circle of a few feet about the nest. The next day he found that the spider had brought moss from outside the cleared space and covered the trap-door with it, thus making it very conspicuous in the cleared ground space. The spider's instinct was not capable of that quick modification to allow it to do what a reasoning animal would have done-namely, covcred the trap-door only with soil to make it resemble the cleared ground about it.

Another interesting nest-making spider is the turretspider, that builds up a little tower (Fig. 158) of sticks and soil and moss above its burrow. The sticks of which this burrow are built are an inch or two in length, and are arranged in such manner as make the turret five-sided. The sticks are fastened together with silk, and the turret is made two or three inches high. This turret-building spider is one of those that carry about their egg-cocoon with them. A female of this spider in captivity was observed to pay much attention to caring for this cocoon.