Fig.9 A large branching nerve-cell Fig. 9—A large branching nerve-cell, or “soul-cell”, from the brain of an electric fish (_Torpedo_). In the middle of the cell is the large transparent round _nucleus,_ one _nucleolus,_ and, within the latter again, a _nucleolinus._ The protoplasm of the cell is split into innumerable fine threads (or fibrils), which are embedded in intercellular matter, and are prolonged into the branching processes of the cell (_b_). One branch (_a_) passes into a nerve-fibre. (From _Max Schultze._) Fig.10 Blood-cells, multiplying by direct division Fig. 10—Blood-cells, multiplying by direct division, from the blood of the embryo of a stag. Originally, each blood-cell has a nucleus and is round (_a_). When it is going to multiply, the nucleus divides into two (_b, c, d_). Then the protoplasmic body is constricted between the two nuclei, and these move away from each other (_e_). Finally, the constriction is complete, and the cell splits into two daughter-cells (_f_). (From _Frey._) The intricate physiological processes which accompany this “mitosis” have been very closely studied of late years. The inquiry has led to the detection of certain laws of evolution which are of extreme importance in connection with heredity. As a rule, two very different parts of the nucleus play an important part in these changes. They are: the _chromatin,_ or coloured nuclear substance, which has a peculiar property of tingeing itself deeply with certain colouring matters (carmine, hæmatoxylin, etc.), and the _achromin_ (or _linin,_ or _ achromatin_), a colourless nuclear substance that lacks this property. The latter generally forms in the dividing cell a sort of spindle, at the poles of which there is a very small particle, also colourless, called the “central body” (_centrosoma_). This acts as the centre or focus in a “sphere of attraction” for the granules of protoplasm in the surrounding cell-body, and assumes a star-like appearance (the cell-star, or _monaster_). The two central bodies, standing opposed to each other at the poles of the nuclear spindle, form “the double-star” (or _amphiaster,_ Fig. 11, B C). The chromatin often forms a long, irregularly-wound thread—“the coil” (_spirema,_ Fig. A). At the commencement of the cleavage it gathers at the equator of the cell, between the stellar poles, and forms a crown of U-shaped loops (generally four or eight, or some other definite number). The loops split lengthwise into two halves (B), and these back away from each other towards the poles of the spindle (C). Here each group forms a crown once more, and this, with the corresponding half of the divided spindle, forms a fresh nucleus (D). Then the protoplasm of the cell-body begins to contract in the middle, and gather about the new daughter-nuclei, and at last the two daughter-cells become independent beings.