. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 310 BULLETIN OF THE Owing to the opacity of the cells in Unio (pp. 213-216) they were studied with the aid of sections. Only embryos consisting of about twenty cells were used. The nuclear plate is found by study of cross sections to be formed, not of an annular series of granules (Korner- kranz), but by a continuous disk (durchgehende Kornerscheibe). The author does not mention any inequality in the distribution of the granules, such as is exhibited in Limax, nor does his figure [loc. cit, Taf. VIL Fig. 18 6
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 310 BULLETIN OF THE Owing to the opacity of the cells in Unio (pp. 213-216) they were studied with the aid of sections. Only embryos consisting of about twenty cells were used. The nuclear plate is found by study of cross sections to be formed, not of an annular series of granules (Korner- kranz), but by a continuous disk (durchgehende Kornerscheibe). The author does not mention any inequality in the distribution of the granules, such as is exhibited in Limax, nor does his figure [loc. cit, Taf. VIL Fig. 18 6) make the granules of the "Kernplatte" more con- spicuous than those of the surrounding protoplasm. The poles of the spindle are much more marked, on account of their great refractive power, than in plant cells. The rays of the protoplasm converging toward them are very distinct in animal cells, hardly traceable in plant cells. The two segments resulting from a division of the nuclear plate are found in different cells at varying distances from each other. In- terzonal filaments are neither increased in number, nor suffer a lateral expansion, as in plant cells. In some of Strasburger's figures (e. g. Taf. VII. Fig. 20) both ends of the spindle appear broadly truncate after the separation of the segments of the nuclear plate, and each trun- cate face occupying the centre of its aster is marked by a conspicuous structure in which the nuclear fibres terminate. Following this condition is a stage in which the new nuclei are homo- geneous. The latter never occupy the centre of the sun, but often ro- tate, as it were, about the former pole without reaching it. In this w^ay two contemporaneously formed nuclei may eventually lie (as in Stras- burger's Fig. 10, Taf. VIII.) farther apart than the centres of the two asters. In all animal cells which he has had the opportunity of study- ing, Strasburger finds that the new nucleus becomes at first homogene- ous by the confluence
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