The cell in development and inheritance . vage into fourequal blastomeres, each of which receives one of the centrosomes. 1 Cf. p. 307. 356 CELL-CHEMISTRY AND CELL-PHYSIOLOGY The latter must, therefore, be the centres of division ; ^ though itmust not be forgotten that, in some cases at any rate, normal divisionrequires the presence of nuclear matter (p. io8). The centrosome must, however, be something more than a meredivision-centre; for, on the one hand, in leucocytes and pigment-cellsthe astral system formed about it is devoted, as there is good reasonto believe, not to cell-division, but t
The cell in development and inheritance . vage into fourequal blastomeres, each of which receives one of the centrosomes. 1 Cf. p. 307. 356 CELL-CHEMISTRY AND CELL-PHYSIOLOGY The latter must, therefore, be the centres of division ; ^ though itmust not be forgotten that, in some cases at any rate, normal divisionrequires the presence of nuclear matter (p. io8). The centrosome must, however, be something more than a meredivision-centre; for, on the one hand, in leucocytes and pigment-cellsthe astral system formed about it is devoted, as there is good reasonto believe, not to cell-division, but to movements of the cell-body as awhole; and, on the other hand, as we have seen (pp. 165, 172), it isconcerned in the formation of the fiagella of the spermatozoa andspermatozoids, and probably also in that of cilia in epithelial (97) was thus led to the conclusion that the centrosomeis essentially a mass of kinoplasni, the active motor plasm,^ anda nearly similar view has been adopted by several recent A B C Fig. 166. — Cleavage of dispermic egg of Toxopneustes. A. One sperm-nucleus has united with the egg-nucleus, shown at a. b.; the other lies sperm-asters have divided to form amphiasters {a. b. and c. d.). B. The cleavage-nucleus,formed by union of the three germ-nuclei, is surrounded by the four asters. C. Result of the firstcleavage, the four blastomeres lettered to correspond with the four asters. Henneguy concludes that the centrosomes are motor centres ofthe kinoplasm both for external and for internal manifestations.^Lenhossek regards them as motors for the control of ciliary actionas well as for that of the spermatozoon,* and perhaps also for that ofmuscle-fibrillae.^ Zimmerman concludes that the microcentrum isthe motor centre of the cell, that is, the kinocentrum opposed tothe nucleus as the chemocentrum. ^ Regarding their control ofciliary action, he makes the same suggestion as that of Henneguy andLenhossek cited a
Size: 2760px × 905px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1902
