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While instinct culminates in insects, the highest development of intelligence is presented in man.157 In man only does instinct cease to be the controlling power. He stands alone in having the whole of his organization conformed to the demands of his brain; and his intelligent acts are characterized by the capacity for unlimited progress. The brutes can be improved by domestication; but, left to themselves, they soon relapse into their original wildness. Civilized man also goes back to savagery; yet man (though not all men) has the ambition to exalt his mental and moral nature. He has a soul, or conscious relation to the infinite, which leads him to aspire after a lofty ideal. Only he can form abstract ideas. And, finally, he is a completely selfdetermining agent, with a prominent will and conscience -the highest attribute of the animal creation. In all this, man differs profoundly from the lower forms of life.

3. The Voices of Animals

Most aquatic animals are mute. Some crabs make noises by rubbing their fore legs against their carapace; and many fishes produce noises in various ways, mostly by means of the swim bladder. Insects are the invertebrates which make the most noise. Their organs are usually external, while those of vertebrates are internal. Insects of rapid flight generally make the most noise. In some the noise is produced by friction (stridulation); in others, by the passage of air through the spiracles (humming). The shrill notes of crickets and grasshoppers are produced by rubbing the wings against each. other, or against the thighs; but the cicada, or harvest fly, has a special apparatus - a tense membrane on the abdomen, acted upon by muscles. The buzzing of flies and humming of bees are caused, in part, by the vibra

tions of the wings; but the true voice of these insects comes from the spiracles of the thorax.

Snakes and lizards have no vocal cords, and can only hiss. Frogs croak 158 and crocodiles roar, and the huge tortoise of the Galapagos Islands utters a hoarse, bellowing noise.

The vocal apparatus in birds is situated at the lower end of the trachea, where it divides into the two bronchi.159 It consists mainly of a bony drum, with a cross bone, having a vertical membrane attached to its upper edge. The membrane is put in motion by currents of air passing on either side of it. Five pairs of muscles (in the songsters) adjust the length of the windpipe to the pitch of the glottis. The various notes are produced by differences in the blast of air, as well as by changes in the tension of the membrane. The range of notes is commonly within an octave. Birds of the same family have a similar voice. All the parrots have a harsh utterance; geese and ducks quack ; crows, magpies, and jays caw; while the warblers differ in the quality, rather than the kind, of note.160 The parrot and mocking bird use the tongue in imitating human sounds. Some species possess great compass of voice. The bellbird can be heard nearly three miles; and Livingstone said he could distinguish the voices of the ostrich and the lion only by knowing that the former roars by day, and the latter by night.

The vocal organ of mammals, unlike that of birds, is in the upper part of the larynx. It consists of four cartilages, of which the largest (the thyroid) produces the prominence in the human throat known as "Adam's apple," and two elastic bands, called "vocal cords," just below the glottis, or upper opening of the windpipe. The various tones are determined by the tension of these cords, which is effected by the raising or lower

Human

ing of the thyroid cartilage, to which one end of the cords is attached. The will cannot influence the contraction of the vocalizing muscles, except in the very act of vocalization. The vocal sounds produced by mammals may be distinguished into the ordinary voice, the cry, and the song. The second is the sound made. by brutes. The whale, porpoise, armadillo, ant-eater, porcupine, and giraffe are generally silent. The bat's voice is probably the shrillest sound audible to human ears. There is little modulation in brute utterance. The opossum purrs, the sloth and kangaroo moan, the hog grunts or squeals, the tapir whistles, the stag bellows, and the elephant gives a hoarse trumpet sound from its trunk and a deep groan from its throat. All sheep FIG. 356.have a guttural voice; all the ox family low, from the bison to the musk ox; all the horses and donkeys neigh; all the cats miau, from the domestic animal to the lion; all the bears growl; and all the canine family — fox, wolf, and dog bark and howl. The howling monkeys and gorillas have a large cavity, or sac, in the throat for resonance, enabling them to utter a powerful voice; and one of the gibbon apes has the remarkable power of emitting a complete octave of musical notes. The human voice, taking the male and female together, has a range of nearly four octaves. Man's power of speech, or the utterance of articulate sounds, is due to his intellectual development rather than to any structural difference between him and the apes. Song is produced by the vocal cords, speech by the mouth.

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Larynx, seen in profile; a, half of the hyoid bone; e, trachea; f, esophagus; g, epiglottis.

DODGE'S GEN. ZOOL. 26

CHAPTER XXII

REPRODUCTION

It is a fundamental truth that every living organism has had its origin in some preëxisting organism. The doctrine of "spontaneous generation," or the supposed origination of organized structures out of inorganic particles, or out of dead organic matter, has not yet been sustained by facts.

Reproduction is of two kinds sexual and asexual. All animals, probably, have the first method, while a very great number of the lower forms of life have the latter also.

Of asexual reproduction there are two kinds - Selfdivision (Fission) and Budding.

Self-division, the simplest mode possible, is a natural breaking-up of the body into distinct surviving parts. This process is sometimes extraordinarily rapid, the increase of one animalcule (Paramecium) being computed at 268 millions in a month. It may be either transverse or longitudinal. Of the first sort, Fig. 10 is an example; of the latter, Fig. 11, a. This form of reproduction is, naturally, confined to animals whose tissues and organs are simple, and so can easily bear division, or whose parts are so arranged as to be easily separable without serious injury. The process is most common in Protozoa, worms, and polyps.

Budding is separated by no sharp line from selfdivision. While in the latter a part of the organs of the parent go to the offspring, in the former one or

more cells of the original animal begin to develop and multiply so as to grow into a new animal like the parent. The process in animals is quite akin to the same operation in plants. The buds may remain permanently attached to the parent stock, thus making a colony, as in corals and Bryozoa (continuous budding), or they may be detached at some stage of growth (discontinuous budding). This separation may occur when the bud is grown up, as in hydra (Fig. 18), or as in plant lice, daphnias (Fig. 56), and among other animals the buds may be internal, becoming detached when entirely undeveloped and externally resembling an egg. They differ, however, entirely from a true egg in developing directly, without fertilization.

Sexual Reproduction requires usually from different animals. cell or egg, and the sperm cell.

cells of two kinds, These are the germ

The embryo is devel

oped from the cells which are formed by the repeated divisions of the ovum which take place as a result of its union with the sperm cell.161

The egg consists essentially of three parts, the germinal vesicle, the yolk, and the vitelline membrane, which surrounds both the first. It is ordinarily globular in shape. Of the three parts, the primary one is the germinal vesiclea particle of protoplasm. The yolk serves as food for this, and the membrane protects both. When a great mass of yolk is present it is divisible into two parts-formative and food yolk. The latter is of a more oily nature than the former, and is usually not segmented with the egg. The structure of the hen's egg is more complicated. The outside shell consists of earthy matter (lime) deposited in a network of animal matter. It is minutely porous, to allow the passage to and fro of vapor and air. Lining the shell is a double membrane (membrana putaminis) resembling delicate

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