. Physiologie générale ; un aperçu de la science de la vie. 194 physiologie générale se compose d'nucleins, organise lui-même en threads qui semblent vaguement regroupés en une bobine (Fig. 72, A). Les filets, qui ont donné à cette forme de division nucléaire le nom de division mitotique et ont environ la même longueur, coupée en deux sur la longueur de façon à ce que l'un de l'un des résultats double fil. En même temps, la membrane nucléaire est dissous, et aux deux pôles opposés de la masse nucléaire les centrosomes, ou des organes centraux (p. 69), entourés de leurs radiations protoplasmique, désormais visible, la tw

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. General physiology; an outline of the science of life. 194 GENERAL PHYSIOLOGY consists of nucleins, arranges itself into threads which appear loosely rolled up into a coil (Fig. 72, A). The threads, which have given to this form of nuclear division the name of mitotic division and have approximately equal lengths, split lengthwise so that from each a double thread results. At the same time the nuclear membrane becomes dissolved, and at the two opposite poles of the nuclear mass the centrosomes, or central bodies (p. 69), surrounded by their protoplasmic radiations, now become visible, the two being united to one another by a fibrous, spindle-shaped figure which is derived from the achromatic substance mixed with the protoplasm. The double threads form loops, and group themselves in the equator of the achromatic nuclear spindle in such a way that their angles are directed towards the centre (Fig. 72, B). Presently the spindle-fibres, streaming out from the centrosomes, by their own contraction divide the double threads in such a way that one half of each is turned to- ward one pole, the other half toward the other (Fig. 72, C). Thus two groups of threads separate from each other and from the equator of the spindle (Fig. 72, D). With this the progressive phase of nuclear division is ended and the retrogressive phase begins. The two groups of chromatic threads proceed further and further toward the two poles, so that the whole equatorial part of the spindle becomes free (Fig. 72, S). Fig. 73.—Centrosomes with Presently the spindle-fibres between the i'n°th?^S^3iorof*the two groups begin to .become indistinct, 'egg-ceii. (After BoYeri.) ^^^^ ^-^^ threads bccome twisted again into a coil at each pole (Fig. 72, F). During this process the whole cell-body has become constricted by a circular groove, the plane of which stands at right angles to the axis of the two nuclear poles, ' The groove becomes deeper and deeper, until finally the whole cell divides into two equal

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