Then if we wish to ascertain, with certainty, the true function of the reproductive organs in man, we must pursue the course above indicated; in other words, study the function of reproduction in lower animals. We say _lower animals_, because man is really an animal, a member of the great animal kingdom, though not a beast--at least he should not be a beast, though some animals in human form approach very closely to the line that separates humanity from brutes. We are brought, then, for a solution of this problem, to a consideration of the question, What is the object of the reproductive act in those members of the animal kingdom just below man in the scale of being? Let science tell us, for zoologists have made a careful study of this subject for centuries. We quote the following paragraphs from one of the most distinguished and reliable of modern physiologists;[11] the facts which he states being confirmed by all other physiologists:-- "Every living being has a definite term of life, through which it passes by the operation of an invariable law, and which, at some regularly appointed time, comes to an end.... But while individual organisms are thus constantly perishing and disappearing from the stage, the particular kind, or species, remains in existence.... This process, by which new organisms make their appearance, to take the place of those which are destroyed, is known as the process of _reproduction_ or _generation_. "The ovaries, as well as the eggs which they contain, undergo, at particular seasons, a periodical development, or increase in growth.... At the approach of the generative season, in all the lower animals, a certain number of the eggs, which were previously in an imperfect and inactive condition, begin to increase in size and become somewhat altered in structure." "In most fish and reptiles as well as in birds, this regular process of maturation and discharge of eggs takes place but once in a year. In different species of quadrupeds it may take place annually, semi-annually, bi-monthly, or even monthly; but in every instance it recurs at regular intervals, and exhibits accordingly, in a marked degree, the periodic character which we have seen to belong to most of the other vital phenomena." "In most of the lower orders of animals there is a periodical development of the testicles in the male, corresponding in time with that of the ovaries in the female. As the ovaries enlarge and the eggs ripen in the one sex, so in the other the testicles increase in size, as the season of reproduction approaches, and become turgid with spermatozoa. The accessory organs of generation, at the same time, share the unusual activity of the testicles, and become increased in vascularity and ready to perform their part in the reproductive function."