In order to form an approximate conception of the organisation of those ancestors of Man which first developed out of the single-celled Primæval animals, it is necessary to trace the changes undergone by the human egg in the beginning of its individual development. It is just here that ontogeny guides us with the greatest certainty on to the track of phylogeny. We have already seen that the egg of Man (in the same way as that of all other Mammals), after fructification has taken place, falls by self-division into a mass of simple and equi-formal Amœba-like cells (vol. i. p. 190, Fig. 4 _D_). All these divided globules are at first exactly like one another, naked cells containing a kernel, but without covering; in many animals they show movements like those of the Amœbæ. This ontogenetic stage of development which we called Morula (p. 125), on account of its mulberry shape, is _a certain proof_ that in the early primordial period there existed ancestors of man which possessed the _form value_ of a mass of homogeneous, loosely connected cells. They may be called a _community of Amœbæ_ (Synamœbæ). (Compare p. 127.) They _originated_ out of the single-celled Primæval animals of the second stage by repeated self-division and by the permanent union of the products of this division. FOURTH STAGE: +Ciliated Larva (Planæada)+. In the course of the ontogenesis of most of the lower animals, and also in that of the lowest Vertebrate animals, the Lanceolate Animals, or Amphioxus, there first develops out of the Morula (Frontispiece, Fig. 3) a ciliated larva (planula). Those cells, lying on the surface of the homogeneous mass of cells, extend hair-like processes, or fringes of hairs, which by striking against the water keep the whole body rotating. The round many-celled body thus becomes differentiated, in that the external cells covered with cilia differ from the non-ciliated internal cells (Frontispiece, Fig. 4). In Man and in all other Vertebrate animals (with the exception of the Amphioxus), as well as in all Arthropoda, this stage of the ciliated larva has been lost, in the course of time, by abbreviated inheritance. There must, however, have existed ancestors of Man in the early Primordial period which possessed the form value of these ciliated larvæ (Planæa, p. 125). A certain proof of this is furnished by the Amphioxus, which is on the one hand related by blood to Man, but on the other has retained down to the present day the stage of the planula. FIFTH STAGE: +Primæval Stomach Animals (Gastræada)+.