Multicellular animals--Man, for example--grow embryologically by Mitosis or Indirect Division. As in Direct Division, typically, the nucleus in mitosis splits first and the cytoplasm secondly; but before the nucleus divides its content undergoes a series of changes. The chromatin loses its reticular arrangement and gives rise to a definite number of separate bodies, usually rod-shaped, known as Chromosomes. In this process the chromatin becomes a convoluted thread, called the Skein or Spireme. The thread thickens and opens out somewhat, and finally breaks transversely to form the chromosomes, which may be rods, straight, curved, ovoid, and sometimes annular. Commonly the nuclear material fades away and leaves the chromosomes in the cell-plasm. (Fig. II, 2 and 3.) [Illustration: Fig. II DIAGRAM OF MITOSIS. 1. Cell with resting Nucleus. 2. Prophase: Chromatin in thickened convoluted threads, beginning of Spindle. 3. Prophase: Chromosomes. 4. Prophase: Spindle in long axis of the Nucleus, Chromosomes dividing. 5. Anaphase: Chromosomes moving toward the Centrosomes. 6. Chromosomes at the poles forming the Diaster, beginning splitting of the Cell-body. 7. Telophase, Daughter-Nuclei returning to resting state. 8. Daughter-Nuclei showing Monaster below. 9. The two new Cells.] It is almost an established fact that each species of animal and plant has a fixed and characteristic number of chromosomes, which regularly recurs in the division of all its cells. In forms arising by sexual production the number is even. The number of chromosomes in the human cell is said to be forty-eight. There are, according to some observers, forty-seven chromosomes in man and forty-eight in woman. There seem to be twice as many chromosomes in white men as in negroes. Wilson gives the number[30] of specific chromosomes for seventy-four animals and plants. Germ-cells as differentiated from the somatic cells have in the perfected cell always half the number of chromosomes found in a somatic cell. [30] _The Cell in Development and Inheritance_, p. 207. While these changes are going on in the chromatin the Amphiaster forms. This consists of a fibrous spindle-shaped body, the Spindle, at either pole of which is an Aster made up of rays. In the centre of each aster is a Centrosome, and this may have a Centrosphere about it. As the amphiaster grows the centrosomes are grouped in a plane at the equator of the spindle, forming the Equatorial Plate. (Fig. II, No. 4.) The process so far makes up the Prophases of the Mitosis.