The first living organisms formed their hierarchies thus: individual unicellular, or plastide; group of plastides or meride. The merides, as the protozoaires, can reproduce themselves asexually, or by division or budding. They may separate completely or remain attached to their generator. If they remain attached one has mounted a step and attained the zoide. Thence, by colonies of zoides one gets individuals still more complex, called demes. None of these terms is much more than a convenience for memory. The nomenclature stops, as does the progression, at a certain moment, for the evolution has its limit, its finality, as does even the milieu in which life continues to evolve. One might say that heaving up from the obscure vital centre, the new animal-shoots branch upward until they knock their heads upon an ideal or imaginary roof which prevents any further climbing. This is the death of the species, and Nature contemptuously abandoning her work, begins to mate yet another mould of the initial ooze, to derive from it a new form. The dream of an unlimited transformation of actual species is pure chimæra; they will disappear one by one, according to their order of primogeniture, according to their faculty for adapting themselves to the changing milieu, and one might foresee, if the earth lasts, in a distant time an unimaginable fauna replacing the present fauna, and even replacing man. Man is a metazoaire, that is to say an animal with differentiated pluricellules, like the sponge, the wheel animals, and the annelids. He belongs to the artizoaire series: a head, belly, back, bilateral symmetry; to the vertebrate branch: internal skeleton, cartilaginous and osseous; to the class of mammifers, to the sub-class of placentaires; to the group of primates not far from the chiroptera (bats) and the rodents.