ration here is only partial. Preceding the condition represented by the hydra, and connecting with the last (d), we ought to find one in which two similar cells elaborated by the same organ unite or conjugate to commence the new life—a condition in which the sexual elements are potentially but not visibly differentiated. This condition is realized, as far as we yet know, only in the conjugation of unicelled organisms.
(f.) Bisexuality.—The next step is of course the complete differentiation not only of the sexual elements, but also of the sexual organs. This is bisexuality or hermaphroditism, very common, as is well known, among lower animals and almost universal among plants.
(g.) Unisexuality.—The last step is the separation of the sexes in different individuals. This of course effectually prevents self-fertilization in both animals and plants. But cross-fertilization must be insured. This, as already seen, is done by winds and insects in the case of plants, and by waves and currents in some lower animals. These agents do not, however, insure fertilization in higher animals. Therefore, in them there is added sex-appetite and all associated feelings for that purpose.
(h.) After the separation of the sexes has been a sufficiently long time accomplished, the evidence in the ontogeny of former conditions is gradually obliterated—the memory of them is lost.
6. Differentiation of the Two Sexual Individuals.—We have now reached complete unisexuality—i. e., the separation of the sexes into different individuals, but not yet the very best results. Unisexuality is better than the orchid and snail method of mutual fertilization, only because the latter method is incapable of further differentiation, and therefore of any further improvement of results. In cases of mutual fertilization the individuals are all alike, except these small individual differences, which occur even in self-fertilizing bisexuals. But as soon as the sexes are separated into different individuals, then there is room for indefinite differentiation of the two sexual individuals. Now, as we go up the animal scale we find that such differentiation has indeed taken place, and that progressively. The sexual differences—i. e., the difference between male and female individuals of the same species—become greater and greater as we rise in the scale. They are also greater, we believe, in the higher as compared with the lower races of man, and in the cultivated classes as compared with the uncultivated classes. From this sexual difference springs sexual attractiveness, and from this lowest root, it is not too much to say, springs much if not all our noblest altruistic nature. For, as our physiological functions are primarily divisible into two great groups, viz., the nutritive and the reproductive, the one including all that assemblage of functions which conserve the individual life, the other all that assemblage of functions which conserve the continuous life of the species, so all our psychical functions are also primarily divisible into two groups, the egoistic and
