Upon referring to Biology--on the processes whereof every development, both physical and psychical, of living creatures rests--this curious dual constitution of the body, together with the problems of dual sex-transmission and inherency, become explicable. And the solutions are at the same time so simple and inevitable as to be the strongest possible confirmation of my thesis. As already stated, living organisms, offspring of two parents, derive half the source of their structure from one parent, half from the other. All plants and living creatures evolve their organisation from a single microscopic cell, precisely as Life itself evolved primarily, and has developed out of the single-celled, microscopic _amoeba_. The microscopic cell which develops into a living creature is composed thus of two halves, or "gametes," to employ the scientific term. One half was contributed by the father: the other, by the mother. The two have united to form a whole cell. From such a cell (zygote), half male, half female, the body of every living organism has sprung. Now, although these two half-cells unite to form a whole cell, exchange constituents, and appear to lose their identity each in the other, it is, in the face of the strange dual constitution of the body, difficult to doubt that each half actually retains its identity and sex-inherences, and develops along its own lines (albeit in close correlation with the other), throughout all the marvellous, intricate, and complex processes of embryological existence, during which the zygote is evolving into a living creature, capable of separate and individual life. And the inherences of these two halves are represented, at birth, in the respective sides of the body; each being, as it were, a complete and perfect entity, although inseparably knit in one flesh to its twin. And throughout all the further intricate and complex processes whereby the creature comes to maturity, lives, reproduces its species, and dies, each half preserves its individual inherence alike in constitution and in function. And yet in the mystical unity of their commingling duality, they are one flesh.