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, in making the formation of the 

 spindle fibres progress from the poles of the spindle. In relation to the 

 centre of the aster, therefore, they grow like other rays, — in a centrif- 

 ugal direction. Their course, like that of unipolar filaments, is radial, 

 until, by increase of length, the rays from the two stars meet midway 

 to form the continuous bipolar filaments. Their course now becomes 

 slightly bent, so that, collectively, they present the appearance of a 

 cask. 



Thus there exist many features suggestive of the identity of astral 

 rays and the initial condition of spindle fibres. It is a fundamental 

 question whether these fibres are ever constituted in any part of vitelline 



stages of Nephelis : "His preparations show most distinctly what you discovered in 

 the egg of Limax, — curved radial lines. I can but wonder that Hertwig and 

 BiitschH did not recognize the same." 



