"”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 mot 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 unction.”"