The most complex animal proceeds originally from a simple cell; and 'at the two extremes we may contemplate the single germinal membrane of the ovum, which is discharging contemporaneously every function--digesting, absorbing, respiring, etc.; and the complete organic apparatus of man, the stomach, the lungs, the skin, the kidneys, and the liver--mechanisms set apart each for the discharge of a special duty, yet each having arisen, as we know positively from watching the order of their development, from that simple germinal membrane.' (Draper.) This is what one physiologist says of the ovum which is being developed into a complex being. Here is what another says of animals at the lower end of the zoological scale: 'The simplest organisms breathe, exhale, secrete, absorb, and reproduce, by their envelopes alone.' (Lewes.) Here we perceive the resemblance between the ovum of the higher animals and the permanent structure of the lower animals. Indeed, some of the lower forms of animal life are simply cells. How vast the difference between the organism of man, with all its complexity of structure, and that of the Ameba or Actinophrys, which, being merely a homogeneous mass of organic matter, performs all the functions of its simple life without any special organ whatever! Yet, is man any less a unit than the Ameba, or any other simple organism? Does his multiplicity of organs impair the integrity of his anatomical and physiological oneness? Is the circulation independent of respiration? Is digestion independent of the circulation? Can any one organ act independently of the others? Is not the entire series of parts, organs, and functions bound up in complete and inseparable unity? The vicarious action of one organ for another has been a question among physiologists; and if admitted, as in the case of the salivary glands acting for the kidneys in profuse spitting, and the skin for the liver, the vicarious function can only obtain to a slight degree and in a temporary manner. The destruction of any considerable organ involves the destruction of all the rest. I repeat that the integrity of the physiological unity at the top of the scale, is far more complete, with all its complexity, than is the integrity of the physiological unity at the bottom of the scale, with its marked simplicity of structure. By no sort of legerdemain or surgical skill can we make an individual mammal become two. If we divide it, the whole dies. Not so, however, with some of the lower grades of animal existence. Cut a hydra into thirty or forty pieces, and each piece will become a distinct animal--a facsimile of the original one. In quite an analogous way do a large number of animals at the lower end of the scale propagate, by segmentation and division; one individual becoming two, two four, and so on.