. The Biological bulletin. Biology; Zoology; Marine biology. 23O O. C. GLASER. two widely separated lobes, one of which — the lower — has the nuclear membrane equally distinct throughout its circumference. This nucleus was killed in the very act of pulling apart. Other nuclei such as 6, 7, 8, 9, 11 and 12, seem to be dividing by the formation of a granular plate, such as is exhibited by some of the nuclei in Fig. 4. Others, such as 14 and 15, the latter drawn with its clearly marked cell boundaries, give no indication whatever of how the separation may have taken place. The groups 16, 17, 18 a
. The Biological bulletin. Biology; Zoology; Marine biology. 23O O. C. GLASER. two widely separated lobes, one of which — the lower — has the nuclear membrane equally distinct throughout its circumference. This nucleus was killed in the very act of pulling apart. Other nuclei such as 6, 7, 8, 9, 11 and 12, seem to be dividing by the formation of a granular plate, such as is exhibited by some of the nuclei in Fig. 4. Others, such as 14 and 15, the latter drawn with its clearly marked cell boundaries, give no indication whatever of how the separation may have taken place. The groups 16, 17, 18 and 19, are extremely interesting as they seem to throw light on the origin of nuclear nests. Very fre- quently I have found three, four or five nuclei huddled together so closely that I could make out clearly no other relation between them. Often one of them is at a slightly different level from the others. In the cases under consideration the history of such nests may be read. A nucleus instead of dividing into two, in the manner of an amoeba, simply elongates, and becomes lobed in two or more widely separated regions which may or may not be provided with nucleoli. These lobes later separate, and the original nucleus has divided into three or more parts, ap- proximately equal in size or at times quite unequal. That there is nothing anomalous about this mode of division is illustrated by the nuclei in the external kidneys in which one frequently finds these conditions clearly exemplified (Fig. 8). In comparing the nuclei. ABC D Fig. 8. Nuclei from the external kidneys where cases of multiple simultaneous division are frequent. These drawings were made from entire nuclei and show that the divisions are not dependent on the activities of the nucleoli, which may or may not be present. just described with those in the disintegrating entoderm cells, it is clear that, excluding 17, 18 and 19, they are very much smaller in size. Furthermore, the nuclei in Fig. 7 show none of the c
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectb, booksubjectzoology
