The cell in development and inheritance . g numerous small secondary asters and centrosomes, from unfertilized egg of Cerebratulus after 22 hours in % sodium chloride solution. water or treated by weak solutions of sodium or magnesium asters often contain deeply staining, central granules indistin-guishable from the centrosomes of the normal asters; and, what is ofhigh interest, such of them as He near the nucleus take part in theirregular nuclear division that ensues, forming centres toward whichthe chromosomes pass. These divisions continue for some time, thechromosomes be
The cell in development and inheritance . g numerous small secondary asters and centrosomes, from unfertilized egg of Cerebratulus after 22 hours in % sodium chloride solution. water or treated by weak solutions of sodium or magnesium asters often contain deeply staining, central granules indistin-guishable from the centrosomes of the normal asters; and, what is ofhigh interest, such of them as He near the nucleus take part in theirregular nuclear division that ensues, forming centres toward whichthe chromosomes pass. These divisions continue for some time, thechromosomes being irregularly distributed through the &gg, and givingrise to nuclei of various sizes apparently dependent upon the numberof chromosomes each receives. After a variable number of such 3o8 SOME PROBLEMS OF CELL-ORGANIZATION divisions the asters disappear, yet the irregular nuclear divisions con-tinue, nuclear spindles with distinct centrosomes being formed at eachdivision, but apparently without relation to the older asters, and they. Fig. 151. — Formation of centrosomes and asters in unfertilized echinoderm-eggs. \_A, B,Morgan ; C-E, R. Hertwig.] A. Arbacia, after 4% hours in % solution of sodium chloride, then 5 hours in sea-water;scattered chromosomes and asters. B. Asters formed after by^ hours in NaCl. C-E. Echinusafter treatment with % strychnine-solution, showing various forms of astral formations (fan-shaped aster, half spindle, and complete mitotic figure). are believed by Morgan to arise de novo from the egg substance.^In the meantime irregular cleavage of the occurs, though noembryo is produced.^ Loeb, however, in the remarkable experiments 1 99, p. 479. ?^ Morgan makes the important observation, which harmonizes with that of Boveri,reported at page 108, that the divisions occur with 7-espect to the mimber and position of thenuclei, not of the asters, concluding that the former must therefore play an essential rdle ascentres of division, and that the a
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1902
