GENERATION (in Physiology) general° ; Fr. generation; Germ. Zeugung ; Ital, gene razianc ;) is the process by which the young of living bodies are produced, and their spe cies continued. In common language the term is frequently confined to the mere act of union of the sexes of animals; but in general and animal physiology it is generally employed in the more extended signification given to it in the following article, viz. to denote the assem blage of all the functions of animals concerned in the formation of their young, and as syno nymous, therefore, with the function of Repro duction.
In directing our attention to the mode in which the function of reproduction is effected in various classes of animals, so many striking differences present themselves, that we find it difficult if not impossible to point out any general circumstances in respect to which they all agree. Some animals, for example, are propagated by the division of their whole bodies into pieces, each of which by a pecu liar change becomes an independent individual entering upon a new life. Others arise like the parts of a tree by buds which remain for a time attached to the parent stem, and being afterwards separated from it assume an inde pendent existence. A third class of animals have the power of forming and throwing off from their bodies a small portion of organized matter, which, though at the time of its sepa ration from the parent, not resembling it either in form or organization, is yet possessed of the power of living for itself, and, after passing through a variety of successive changes of growth and evolution, of at last acquiring the exact semblance of the parent by which it was produced. In a fourth and last class, com prehending much the greatest number of ani mals, the function of reproduction involves a greater complication of vital processes than in the three other classes above alluded to. The union of two individuals of different sex be comes necessary, and the young owe their origin to the evolution of a more complex organized structure termed the egg, which is formed in and separated from the body of the female parent, and is the product of the union of the male and female of all animals in which the distinction of sex exists. The ovum or egg
is most familiarly known to us in the eggs of domestic birds, to which the product of sexual union in all animals belonging to this fourth class bears a strict analogy in every essential particular.
It may be stated as a general fact, that the reproductive function involves a greater num ber of vital processes in the higher and more complicated than in the lower and simpler kinds of animals. Yet there are exceptions to this rule, and we do not always trace a correspondence between the degree of com plication of the generative process of any animal and the place which that animal holds in the scale of being ; for there are some tribes of animals which are propagated in more than one of the ways above mentioned, and there are some, to which, from the simplicity of their other functions and organization, a low place iu the zoological scale has been assigned, and which nevertheless resemble the higher animals in respect to their mode of reproduction.
A very superficial view, however, of the vari eties of the form obvious in the reproductive process of different animals demonstrates the importance of the reproductive functions in the economy of life, as it points out the intimate relation which these functions bear to the habits, mode of life, and organization of each animal, and spews the infinite care and fore sight with which nature, in every variety of circumstance, has provided for the regular and undisturbed performance of those acts by which the species of organize" beings are con tinued from age to age, in an undeviating suc cession of generations. These facts also fully justify our regarding, along with Cuvier, the reproductive function as constituting one of the fundamental divisions in a classification of the processes of the animal economy.