Comparative anatomy and ontogeny prove beyond question that man is a true vertebrate, and, therefore, man’s special genealogical tree must be connected with that of the other Vertebrates, which spring from a common root with him. But we have also many important grounds in comparative anatomy and ontogeny for assuming a common origin for all the Vertebrates. If the general theory of evolution is correct, all the Vertebrates, including man, come from a single common ancestor, a long-extinct “Primitive Vertebrate.” Hence the genealogical tree of the Vertebrates is at the same time that of the human race. Our task, therefore, of constructing man’s genealogy becomes the larger aim of discovering the genealogy of the entire vertebrate stem. As we now know from the comparative anatomy and ontogeny of the Amphioxus and the Ascidia, this is in turn connected with the genealogical tree of the Invertebrates (directly with that of the Vermalia), but has no direct connection with the independent stems of the Articulates, Molluscs, and Echinoderms. If we do thus follow our ancestral tree through various stages down to the lowest worms, we come inevitably to the _Gastræa,_ that most instructive form that gives the clearest possible picture of an animal with two germinal layers. The Gastræa itself has originated from the simple multicellular vesicle, the _Blastæa,_ and this in turn must have been evolved from the lowest circle of unicellular animals, to which we give the name of Protozoa. We have already considered the most important primitive type of these, the unicellular _Amœba,_ which is extremely instructive when compared with the human ovum. With this we reach the lowest of the solid data to which we are to apply our biogenetic law, and by which we may deduce the extinct ancestor from the embryonic form. The amœboid nature of the young ovum and the unicellular condition in which (as stem-cell or cytula) every human being begins its existence justify us in affirming that the earliest ancestors of the human race were simple amœboid coils. But the further question now arises: “Whence came these first amœbæ with which the history of life began at the commencement of the Laurentian epoch?” There is only one answer to this. The earliest unicellular organisms can only have been evolved from the simplest organisms we know, the _Monera._ These are the simplest living things that we can conceive. Their whole body is nothing but a particle of plasm, a granule of living albuminous matter, discharging of itself all the essential vital functions that form the material basis of life. Thus we come to the last, or, if you prefer, the first, question in connection with evolution—the question of the origin of the Monera. This is the real question of the origin of life, or of spontaneous generation.