The start, then, must be made with a homogeneous mass of protoplasm, such as the existing _Protamoeba primitiva_ of the present day, which is a structureless organism without organs, and which came into existence during the Laurentian period. It is to this simplified condition, as I have previously stated, all fertilized eggs return before they commence to develop. The first process of adaptation effected by the monera must have been the condensation of an external crust, which, as a protecting covering, shut in the softer interior from the hostile influences of the outer world. As soon as, by condensation of the homogeneous moneron, a cell-kernel arose in the interior, and a membrane arose on the surface, all the fundamental parts of the unit were then furnished. Such a unit was an organism, similar to the white corpuscle of the blood, and called _amoebæ_. Here we have two different stages of evolution; the protoplasma (better plasson) of the cytod undergoes differentiation, and is split up into two kinds of albuminous substances--the inner cell-kernel (nucleus) and the outer cell-substance (protoplasma). Edward von Benden, in his work upon _Gregarinæ_, first clearly pointed out this fact, that we must distinguish thoroughly between the plasson of cytods and the protoplasm of cells. An irrefutable proof that such single-celled primæval animals like the amoeba really existed as the direct ancestors of man, is furnished, according to the fundamental law of biogeny, by the fact that the human egg is nothing more than a simple cell. The next step taken in advance is the division of the cell in two;--there arise from the single germinal spot two new kernel specks, and then, in like manner, out of the germinal vesicle two new cell-kernels. The same process of cell-division now repeats itself several times in succession, and the products of the division form a perfect union. This organism may be called a community of _amoebæ_ (synamoebæ). From the community of amoeba morula, now arose ciliated larvæ. The cells lying on the surface extended hair-like processes or fringes of hair, which, by striking against the water, kept the whole body rotating--the lanceolate animals or amphioxus were thus first produced. Here we find from the synamoebæ which crept about slowly at the bottom of the Laurentian primeval ocean by means of movements like those of an amoeba, that the newly-formed planæa by the vibrating movements of the cilia, the entire multicellular body acquired a more rapid and stronger motion, and passed over from the creeping to the swimming mode of locomotion. The planæa consisted, then, of two kinds of cells--inner ones like the amoebæ, and external "ciliated cells." The ancestors of man, which possessed the form value of the ciliated larva, is, of course, extinct at the present day. [Illustration: FIG. I.--The Norwegian Flimmer-ball (Magosphoera Planula), swimming by means of its vibratile fringes; seen from the surface.--_Haeckel._]