. Un manuel de zoologie. Zoologie. Anatomie générale 59 ces animaux être coupées en moitiés anucléés et binucléé, le premier vit et régénère les pièces perdues ; la partie anucléés se déplace pour un temps, semble-t-il aussi longtemps que dure l'énergie stockée, mais il ne peut l'assimiler ou reproduire le portions manquantes et ainsi, tôt ou tard, il meurt. Le centrosome.-Outre le noyau se produit souvent un organe spécial dans le protoplasme, le centrosome, qui, en raison de sa petite taille et un comportement semblable à achromatin en référence à la coloration- fluides, a été longtemps négligée. Répartition Il est bien

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. A manual of zoology. Zoology. GENERAL ANATOMY 59 these animals be cut into nucleate and anucleate halves, the first lives and regenerates the lost parts; the anucleate portion moves about for a time, apparently as long as the stored energy lasts, but it cannot assimilate or reproduce the missing portions and so sooner or later it dies. The Centrosome.—Besides the nucleus there frequently occurs a special body in the protoplasm, the centrosome, which, on account of its small size and a behavior similar to achromatin with reference to staining- fluids, was long overlooked. It is well distributed among the Metazoa, but is absent from most Protozoa, in many of which it appears only at certain times and then disappears. It is probable that it is a derivative of the nucleus, a part of the achromatin which has left the nucleus; in other cases possibly a second nucleus which by degeneration has lost the chro- matin and retained only the motor nuclear substance, the achromatin. In its function the centrosome is a specific organ of cell division which controls both the division of the nucleus and that of the cell itself. Multiplication of Cells.—Increase in cells occurs exclusively by Most common is binary division. division or by budding {gemmation) in which a circular furrow appears on the surface of the cell, deepens and cuts the cell into two equal parts. Mutiple division is more rare and can only occur in multi- nucleate cells. Here the cell divides simultaneously into as many (sometimes hundreds) daughter-cells as there were nuclei present. In all forms of division the similarity of the products is characteristic, while in budding the resulting parts are unequal, one or more smaller daughter- ceUs, the buds, being constricted from a large mother-cell (fig. 21). Direct Cell Division.—Every cell division is accompanied by nuclear division or nuclear division has previously occurred. Direct and indirect division are recognized. Direct division is most common in Pro

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