This theory of development is, then, the opposite of that ordinarily assumed. The latter asserts that increase of growth demands increase of nourishment, whereas this asserts the fact that increase of nourishment determines growth. The struggle for existence is not a struggle for the mere necessaries to maintain life, but a struggle for increase of acquisition, increase of life; it is not a struggle of defence, but an attack which only under certain circumstances becomes a defence. The rule with which we advise our friends is, "Forward! strive to better yourself!" though we may endeavor, in hypocritical spirit, to persuade to contentment those who come into competition with our interests. The chief points, therefore, in which this theory differs from that of Darwin, are as follows:-- "The struggle for existence is really a struggle for increase of nourishment, of life; and independent of the supply of the moment, it goes on at all times, hence even in a state of abundance. "Limitation of supply by competition leads to fixation of the species and, in the end, to its decrease and disappearance. "Sickness, climate, and direct enemies are the destructive agencies, and must secure more propitious conditions for survivors, the stronger their effect. "Only under conditions of prosperity can the survivors propagate largely, and perfect themselves, separating into varieties and species. "The increase and differentiation of the organic world shows us that conditions of prosperity have been the rule, those of want the exception." Rolph's extremely interesting chapter on Propagation traces the sexual instinct to the "mechanical hunger." The earliest example which may be adduced in support of this theory is that of the zooespores which, by copulation, sustain life for a time under the unfavorable conditions of darkness, the thinner male representing, as does also the spermatozooen, the seeking individual suffering from want, the female representing a means of sustenance. The sex of the young organism is in like manner referred by Rolph to conditions of nourishment during development. We now come to the chapter on ANIMAL OR NATURAL ETHICS