The doctrine, therefore, has its scope limited only by biologic data. It of necessity begins with the cell itself in its relation to other cells of that practically compound organism which constitutes a single vertebrate. The cell may, therefore, degenerate as a single member of that organism, producing danger or benefit to the other cells. Thus the cancer cell degenerates in its power of reproduction below the tissue to which it belongs. It is peculiarly true here, as has been said by Herbert Spencer, that every vertebrate is an aggregate whose internal actions are adapted to counterbalance its external actions; hence the preservation of its movable equilibrium depends upon its development and the proper number of these actions; the movable equilibrium may be ruined when one of these actions is too great or too small, and through deficiency or need of some organic or inorganic cause in its surroundings. Every individual can adapt itself to these changeable influences in two ways, either directly or by producing new individuals who will take the place of those whom the equilibrium has destroyed. Therefore there exist forces preservative and destructive of the race. As it is impossible that these two kinds of force should counterbalance each other, it is necessary that the equilibrium should re-establish itself in an orderly way. Since there are two preservative forces of every animal group--the impulse of every individual to self-preservation and the impulse to the production of other individuals--these faculties must vary in an inverse ratio; the former must diminish when the second augments. Degeneration constitutes a process of disintegration, the reverse of integration. Hence, if the term individuation be applied to all the processes which complete and sustain the life of the individual, and that of generation to those which aid the formation and development of new individuals, individuation and generation are necessarily antagonistic. In the phenomena of unisexual generation we see that the larger organisms never reproduce themselves in the unisexual way, while the smaller organisms reproduce themselves with the greatest rapidity by this method. Between these two extremes unisexual reproduction decreases while the size increases. In the history of all plants and animals is evident the physiologic truth, that while the general growth of the individual proceeds rapidly, the reproductive organs remain imperfectly developed and inactive. On the contrary, the principle of reproduction indicates decrease in the intensity of growth and becomes a cause of cessation. Great fecundity is always attended by great mortality. Each superior degree of organic evolution is accompanied by an inferior degree of fecundity. The greater the germs the less is the individuation, and _vice versâ_. The greater and more complex the organisation, the less is the power of multiplication.