. The cell; outlines of general anatomy and physiology. Fig. 151.—Various germinal stages of Closterium. (After Klebahn, PI. XIII., Figs. 6b, 8,9, 11, 13.) (Fig. 151 III). Thus the germinal nucleus divides into fournuclei, by means of two divisions, the second of which succeeds thefirst without a pause (Fig. 151 IV). Meanwhile the protoplasm of the zygote has divided into twohemispheres (Fig. 151 IV), each of which contains two nuclei,which have been produced by the division of one spindle. Thetwo nuclei soon develop differences in appearance, the one (ac-cording to Klebahn, the large nucleus)
. The cell; outlines of general anatomy and physiology. Fig. 151.—Various germinal stages of Closterium. (After Klebahn, PI. XIII., Figs. 6b, 8,9, 11, 13.) (Fig. 151 III). Thus the germinal nucleus divides into fournuclei, by means of two divisions, the second of which succeeds thefirst without a pause (Fig. 151 IV). Meanwhile the protoplasm of the zygote has divided into twohemispheres (Fig. 151 IV), each of which contains two nuclei,which have been produced by the division of one spindle. Thetwo nuclei soon develop differences in appearance, the one (ac-cording to Klebahn, the large nucleus) becoming large and vesi-cular, whilst the other (the small nucleus) remains small, andfinally quite disappears. The small nucleus becomes much moreintensely stained than the large one. It seems to me that theformer disintegrates and dissolves, just like the fragments of thechief nucleus and the subsidiary spindles in Infusoria. Before. THE VITAL PROPERTIES OF THE CELL 281 the process of dissolving is quite completed, thetwo halves of the zygote gradually assume theshape of a Closterium cell (Fig. 152). What is the significance of this seconddivision, which occurs immediately after thefirst, without any intermediate resting stage ?It appears to me that by its means the sameresult is obtained, although in a differentmanner, as is produced by the division, with fig. 152. — Tworeduction, which occurs during the maturing Ciostena, winch have ° ° developed from a ot egg and sperm-cells. In both cases by zygospore, beforemeans of the double division the nuclear sub- they have escaped , . ij 1 ie n ,i > -j from their enclosing stance is reduced to one halt of that contained a normal nucleus, and thus an increase ofnuclear substance is avoided when, in consequence of fertilisation,two nuclei coalesce. Similarly in Desmidiacese a reduction ofnuclear substance occurs after fertilisation, and thus the doublea
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