There is no doubt that the males and females of a race of animals develop out of the same germinal-matter. Its development depends upon two important factors, the impulse, and the capacity to take up matter conditioned thereby. By taking up matter the substance of the newly developed cells is increased, and this in turn prompts them to repeated division, until at last an organ is developed. The new organ again furnishes new impulses, and so influences the development of other organs. The impulses are of themselves physical and chemical. (Haacke.) In the ovule and the embryo the impulses are what chiefly bring about new growth. These impulses the ovum receives from the mother whose product it is. Now, as of the most different impulses now one and now another comes to the front, the embryo will acquire at this time rather these qualities, and at that time those. The impulse will occasion now a greater addition of matter to this organ, and now a greater addition of matter to that. According to observations made up to the present time, there is hardly any doubt that the development of the organs of sex requires an impulse as does the development of all the other organs. These sex-determining impulses originate, like the other development-determining influences, from the mother, since it is she that supplies to the embryo, as agencies of impulse, the juices derived from the food which she has taken. In addition to these, the embryo receives also from the mother such products as are required for the growth that follows the impulse. If the mother gives the child no material for growth and no impulse, then the child, since it is dependent upon the mother, must perish. Now, according as a developing ovum or an embryo either receives the juice, the means of impulse, for the acquisition of the male sex, or for the acquisition of the female sex, so will a male or a female result. * * * * *