Reproduction and generation--Sexual and asexual reproduction--Superfluous growth--Monogony--Self-cleavage--Budding--Formation of spores--Amphigony--Ovum and sperm-cell--Hermaphrodite formation and separation of the sexes--Hermaphrodism and gonochorism of the cells--Monoclinism and diclinism--Monœcism and diœcism--Alternation of sex-division--Sexual glands of the histona--Hermaphroditic glands--Sexual ducts--Generative organs--Parthenogenesis--Pædogenesis--Metagenesis--Heterogenesis-- Strophogenesis--Hypogenesis--Hybridism--Generation of hybrids and the species--Graduation of forms of reproduction. While nutrition secures the maintenance of the organic individual, reproduction insures that of the organic species, or the group of definite forms which we distinguish from others by the name "species." All individuals are more or less restricted in the duration of their lives, and die off after the lapse of a certain time. The succession of individuals, connected by reproduction and belonging to a species, makes it possible for the specific form itself to last for ages. In the end, however, the species is temporary; it has no "eternal life." After existing for a certain period, it either dies or is converted by modification into other forms. The rise of new individuals by reproduction from parent organisms is a natural phenomenon with definite time-restriction. It cannot have continued from eternity on our planet, as the earth itself is not eternal, and even long after its formation was incapable of supporting organic life on its surface. This only became possible when the surface of the glowing planet had sufficiently cooled for liquid water to settle on it. Until this stage carbon could not enter into those combinations with other elements (oxygen, hydrogen, nitrogen, and sulphur) which led to the formation of plasm. As I intend to deal with this process of _archigony_, or spontaneous generation, in a special chapter, I leave it for the present, and confine myself to the study of _tocogony_, or parental generation. * * * * *