REPRODUCTION.
Every individual derives existence from a parent, which word literally means one who brings forth. We restrict the meaning of the term reproduction, ordinarily, to that function by which living bodies produce other living bodies similar to themselves. Production means to bring forth; reproduction, the producing again, or renewing. To protract individual existence, nutrition is necessary, because all vital changes are attended by wear and waste. Nutrition is always engaged in the work of reparation. Every organism that starts out upon its career of development depends upon nourishing materials for its growth, and upon this renewing process for its development. Nutrition is all the while necessary to prolong the life of the individual, but at length its vigor wanes, its functions languish, and, finally, the light of earthly life goes out. Although the single organization decays and passes away, nevertheless the species is uninterruptedly continued; the tidal wave of life surges higher on the shores of time, for reproduction is as constant and stable as the attractive forces of the planetary system.
It is a fact, that many species of the lower order of animals which once existed are now extinct. It has been asserted and denied, that fossil remains of man have been found, indicating that races which once existed have disappeared from the face of the earth. The pyramids are unfolding a wonderful history, embracing a period of forty-five hundred years, which the world of science receives as literally authentic, and admits, also, that fifty-four hundred years are probably as correctly accounted for. The extinction of races is not at all improbable. At the present time, the aboriginal inhabitants of this continent seem to be surely undergoing gradual extinguishment! It, therefore, seems to be possible for a weaker race to deteriorate, and finally become extinct, unless the causes of their decadence can be discovered and remedied. All people are admonished to earnestly investigate the essential conditions necessary for their continuance, for the rise and fall of nations is in obedience to natural principles and operations. Viewed from this standpoint, it is possible that a careful study of the human temperaments and their relations to reproduction may be of greater moment than has hitherto been supposed, and a proper understanding of them may tend to avert that individual deterioration, which, if suffered to become general, would end in national disaster and the extinction of the race.
Until recently, even naturalists believed that descendants were strictly like their parents in form and structure. Now it is known that the progeny may differ in both form and structure from the parent, and that these may produce others still more unlike their ancestry. But all these peculiar and incidental deviations finally return to the original form, showing that these changes have definite limits, and that the alterations observe a specific variableness, which is finally completed by its assuming again the original form. (See [page 16], Figs. 2 and 3).
Reproduction may be sexual or non-sexual. In some plants and animals it is non-sexual. The propagation of species is accomplished by buds. Thus the gardener grafts a new variety of fruit upon an old stock. The florist understands how to produce new varieties of flowers, and make them radiantly beautiful in their bright and glowing colors. The bud personates the species and produces after its kind. Some of the annelides, a division of articulate animals, characterized by an elongated body, formed of numerous rings or annular segments, multiply by spontaneous division. A new head is formed at intervals in certain segments of the body. (See Fig. 97).
Something similar to this process of budding, we find taking place in a low order of animal organization. Divide the fresh water polyp into several pieces, and each one will grow into an entire animal. Each piece represents a polyp, and so each parent polyp is really a compound animal, an organized community of beings. Just as the buds of a tree, when separated and engrafted upon another tree, grow again, each preserving its original identity, so do the several parts of this animal, when divided, become individual polyps, capable of similar reproduction.
The revolving volvox likewise increases by growth until it becomes a society of animals, a multiple system of individuals. There are apertures from the parent, by which water gains a free access to the interior of the whole miniature series. This monad was once supposed to be a single animal, but the microscope shows it to be a group of animals connected by means of six processes, and each little growing volvox exhibits his red-eye speck and two long spines, or horns. These animals also multiply by dividing, and thus liberate another series, which, in their turn, reproduce other groups.
Generation requires the concurrence of stimuli and susceptibility, and, to perfect the process, two conditions are also necessary. The first is the sperm, which communicates the principle of action; the other is the germ, which receives the latent life and provides the conditions necessary to organic evolution. The vivifying function belongs to the male, that of nourishing and cherishing is possessed by the female; and these conditions are sexual distinctions. The former represents will and understanding; the latter, vitality and emotion. The father directs and controls, the mother fosters and encourages; the former counsels and admonishes, the latter persuades and caresses; and their union in holy matrimony represents one; that is, the blending of vitality and energy, of love and wisdom,—the elements indispensable to the initiation of life under the dual conditions of male and female,—one in the functions of reproduction.
Let us consider the modes of Sexual Reproduction, which are hermaphroditic and dioecious.