“The spermatozoon that conveyed to the egg countless complicated individual and racial characteristics of the father was visible only through a microscope; even the most powerful magnification was not enough to show it as other than a homogeneous body, or to determine its origin; it looked the same in one animal as in another. These factors forced one to the assumption that the cell was in the same case as with the higher form it went to build up: that it too was already a higher form, composed in its turn by the division of living bodies, individual living units. Thus one passed from the supposed smallest unit to a still smaller one; one was driven to separate the elementary into its elements. No doubt at all but just as the animal kingdom was composed of various species of animals, as the human-animal organism was composed of a whole animal kingdom of cell species, so the cell organism was composed of a new and varied animal kingdom of elementary units, far below microscopic size, which grew spontaneously, increased spontaneously according to the law that each could bring forth only after its kind, and, acting on the principle of a division of labour, served together the next higher order of existence.”