the procuring of food, or to the rearing of their young; in other words, they have for their end the preservation of the individual and of the species. It is by instinct that the leopard conceals himself and awaits the approach of his prey. It is equally by instinct that the spider spreads his web to entangle the flies which approach it. 138. Some animals go beyond these immediate precautions; their instinct leads them to make provision for the future. Thus the squirrel lays in his store of nuts and acorns during autumn, and deposits them in cavities of trees, which he readily finds again in winter. The hamster digs, by the side of his burrow, compartments for magazines which he arranges with much art. Finally, the bee, more than any other animal, labors in view of the future; and she has become the emblem of order and domestic economy. 139. Instinct exhibits itself, in a no less striking manner, in the anxiety which animals manifest for the welfare of their anticipated progeny. All birds build nests for the shelter and nurture of their young, and in some cases these nests are made exceedingly comfortable. Others show very great ingenuity in concealing their nests from the eyes of their enemies, or in placing them beyond their reach There is a small bird in the East Indies, the tailor bird (Sylvia sutoria,) which works wool or cotton into threads. with its feet and beak, and uses it to sew together the leaves of trees for its nest. 140. The nest of the fiery hang-bird, (Icterus Baltimore,) dangling from the extremity of some slender, inaccessible twig, is familiar to all. The beautiful nest of the hummingbird, seated on a mossy bough, and itself coated with lichen and lined with the softest down from the cotton-grass or the mullein leaf, is calculated equally for comfort and for escaping observation. An East Indian bird, (Ploceus Philippinus,) not only exhibits wonderful devices in the construction, It security, and comfort of its nest, but displays a still further advance towards intelligence. The nest is built at the tips of long pendulous twigs, usually hanging over the water. is composed of grass, in such a manner as to form a com plete thatch. The entrance is through a long tube, running downwards from the edge of the nest; and its lower end is so loosely woven, that any serpent or squirrel, attempting to enter the aperture, would detach the fibres, and fall to the ground. The male, however, who has no occasion for such protection, builds his thatched dome, similar to that of the female, and by its side; but makes simply a perch across the base of the dome, without the nest-pouch or tube. Fig. 24. 141. But it is among insects that this instinctive solici tude for the welfare of the progeny is every where exhibited in the most striking manner. Bees and wasps not only prepare cells for each of their eggs, but take care, before closing the cells, to deposit in each of them something ap propriate for the nourishment of the future young. 142. It is by the dictate of instinct, also, that vast numbers of animals of the same species associate, at certain periods of the year, for migration from one region to another; as the swallows and passenger pigeons, which are sometimes met with in countless flocks. 143. Other animals live naturally in large societies, and labor in common. This is the case with the ants and bees. Among the latter, even the kind of labor for each member of the community is determined beforehand, by instinct. Some of them collect only honey and wax; while others are charged with the care and education of the young; and still others are the natural chiefs of the colony. 144. Finally, there are certain animals so guided by their instinct as to live like pirates, on the avails of others' labor. The Lestris or Jager will not take the trouble to catch fish for itself, but pursues the gulls, until, worn out by the pursuit, they eject their prey from their crop. Some ants make war upon others less powerful, take their young away to their nests, and oblige them to labor in slavery. 145. There is a striking relation between the volume of the brain compared with the body, and the degree of intelligence which an animal may attain. The brain of man is the most voluminous of all, and among other animals there is every gradation in this respect. In general, an animal is the more intelligent, in proportion as its brain bears a greater resemblance to that of man. 146. The relation between instinct and the nervous system does not present so intimate a correspondence as exists between the intellect and the brain. Animals which have a most striking development of instinct, as the ants and bees, belong to a division of the Animal Kingdom where the nervous system is much less developed than that of the vertebrates, since they have only ganglions, without a proper brain. There is even a certain antagonism between instinct and intelligence, so that instinct loses its force and peculiar character, whenever intelligence becomes developed. 147. Instinct plays but a secondary part in man. He is not, however, entirely devoid of it. Some of his actions are entirely prompted by instinct, as, for instance, the attempts of the infant to nurse. The fact, again, that these instinctive actions mostly belong to infancy, when intelligence is but slightly developed, goes to confirm the two last propositions. CHAPTER FIFTH OF MOTION. SECTION I. APPARATUS OF MOTION. 148. THE power of voluntary motion is the second grand characteristic of animals, (57.) Though they may not all have the means of transporting themselves from place to place, there is no one which has not the power of executing some motions. The oyster, although fixed to the ground, opens and closes its shell at pleasure; and the little coral animal protrudes itself from its cell, and retires again at its will. 149. The movements of animals are effected by means of muscles, which are organs designed expressly for this purpose, and which make up that portion of the body which is commonly called flesh. They are composed of threads, which are readily seen in boiled meat. These threads are again composed of still more delicate fibres, called muscular fibres, (45,) which have the property of elongating and contracting. 150. The motions of animals and plants depend, therefore, upon causes essentially different. The expansion and closing. o the leaves and blossoms of plants, which are their most obvious motions, are due to the influence f ligh, heat moisture, cold, and similar external agents; but all the mo tions peculiar to animals are produced by a cause residing within themselves, namely, the contractility of muscular fibres. 151. The cause which excites nerves, although its nature is Fig. 25. contractility resides in the not precisely understood. We only know that each muscular bundle receives one or more nerves, whose filaments pass at intervals across the muscular fibres, as seen in Fig. 25. It has also been shown, by experi ment, that when a nerve entering a muscle is sev ered, the muscle instantly loses its power of contracting under the stimulus of the will, or, in other words, is paralyzed. 152. The muscles may be classified, according as they are more or less under the control of the will. The contractions of some of them are entirely dependent on the will, as in the muscles of the limbs used for locomotior. Others are quite independent of it, like the contractions of the heart and stomach. The muscles of respiration ordinarily act independently of the will, but are partially subject to t: thus, when we attempt to hold the breath, we arrest, for the mo. ment, the action of the diaphragm. 153. In the great majority of animals, motion is greatly aided by the presence of solid parts, of a bony or horny structure, which either serve as firm attachments to the muscles, or, being arranged so as to act as levers, to in crease the precision and sometimes the force of movements The solid parts are usually so arranged as to form a sub |