. Journal of morphology. ecome muchshorter and less conspicuous, the aster becoming greatly re-duced in size. The red central mass, however, does notdiminish, and at this period its reticular character first becomesclearly apparent (Fig. 3, C). About 30 min. after fertilization the rays again become con-spicuous, and at this stage in favorable specimens the futurespindle-fibers may be clearly seen to penetrate into the seg-mentation-nucleus at either pole, where the membrane fadesaway. The remainder of the nuclear membrane now rapidlydisappears, and the peripheral spindle-fibers appear exactly
. Journal of morphology. ecome muchshorter and less conspicuous, the aster becoming greatly re-duced in size. The red central mass, however, does notdiminish, and at this period its reticular character first becomesclearly apparent (Fig. 3, C). About 30 min. after fertilization the rays again become con-spicuous, and at this stage in favorable specimens the futurespindle-fibers may be clearly seen to penetrate into the seg-mentation-nucleus at either pole, where the membrane fadesaway. The remainder of the nuclear membrane now rapidlydisappears, and the peripheral spindle-fibers appear exactly inits place, so that the spindle as a whole appears to be formedby a direct transformation of the achromatic nuclear substance(including the membrane). Meanwhile the nuclear reticulumis transformed into the chromosomes, and the first cleavage-spindle is formed (Fig. 3, D). To sum up : The central archoplasni-sphere (^^ attractionsphere) of the cleavage-amphiastcr is derived by direct ajid No. I.] THE ECHINODERM EGG. 329.
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Keywords: ., bookcentury1800, bookdecade1, booksubjectphysiology, bookyear1887
