. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 536 BULLETIN OF THE Nuclear Spindle. — The fibrous cords which collectively form what Biitschli named the " spindle-shaped body " are intimately connected in their origin with the asters. But to claim that they have only the same significance as the rays of the latter, is not warranted by the observa- tions. They are not only thicker, but they also pursue a difi'erent course not strictly radial, and they exhibit special accumulations of readily stainable substance; they are principally composed of n
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 536 BULLETIN OF THE Nuclear Spindle. — The fibrous cords which collectively form what Biitschli named the " spindle-shaped body " are intimately connected in their origin with the asters. But to claim that they have only the same significance as the rays of the latter, is not warranted by the observa- tions. They are not only thicker, but they also pursue a difi'erent course not strictly radial, and they exhibit special accumulations of readily stainable substance; they are principally composed of nuclear substance, — the rays of vitelline protoplasm. While, then, I cannot agree with Fol that the spindle fibres (bipolar filaments) are not dif- ferent from the unipolar filaments of the aster, and that they appear different simply because enveloped in a different medium, there are still grounds for a comparison. Since the centre of the aster, when it begins to appear, often lies entirely outside the nucleus, the rays must, in such cases, at first be formed exclusively in the yolk, and those which project toward the nucleus are composed of vitelline protoplasm, as well as those which radiate in other directions. The further growth of the aster in the direction of the nucleus is really an encroachment of the vitelline substance on the nuclear territory, just as 0. Hertwig has shown to be the case with the germinative vesicle and first maturation spindle in Asteracanthion. Conditions such as are shown in Fig. 85, Limax, also afford strong evidence that in the beginning the rays which eventually become spindle fibres are formed like the remaining rays of the aster. They are rays which are formed outside the nucleus, or com- mence outside, and, as it were, push their way into that structure. But with that invasion is coupled the metamorphosis of the nucleus, so that the latter is not to be regarded as simply a passive participant in the changes. All accounts agree, I believe
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