332 KING. [Vol. XVII. 



of the massed ends of the radiating fibers. The rays increase 

 quickly in number, and they extend out in every direction, 

 pushing the pigment layer before them (Fig. 53). Their 

 course is no longer marked by pigment granules, as in the 

 earlier stages. 



At the sides towards the segmentation nucleus, certain rays 

 from each astrosphere grow more rapidly than the others (Fig, 

 53). These rays meet, forming the central spindle, in which 

 the segmentation nucleus lies with its membrane still intact. 

 The spindle rays seem to fuse completely in the equatorial 

 region, so that the fibers of the fully formed spindle appear to 

 extend unbroken from pole to pole where they, too, run into 

 the central mass of the astrosphere. 



A similar origin of the segmentation spindle is described by 

 MacFarland ('97) in the egg of Pleurophyllidia californica. 

 Here, after the division of the sperm-centers, the two daughter 

 spheres with their radiating systems separate, showing no visi- 

 ble connection between them. The rays from both centers 

 then completely disappear for a time, but they appear again 

 later, and a central spindle is formed by a fusion of definite 

 rays from each center. 



Opposed to the general acceptance of the cytoplasmic nature 

 of the spindle are the views of Flemming ('80), Moore ('96), 

 and Erlanger ('96), which ascribe to the spindle a dual origin : 

 its superficial portion and its extreme ends originating in the 

 cytoplasm, while its greater internal and equatorial mass arises 

 from the substance of the segmentation nucleus. 



In the egg of Bufo it is not improbable that a part of the 

 substance from the segmentation nucleus goes into the equato- 

 rial mass of the spindle, as the nuclear membrane breaks down 

 before the spindle is completely formed. However, the spindle 

 is primarily of cytoplasmic origin, as clearly demonstrated by 

 Hermann ('91) in the spermatocytes of Salamander, and its par- 

 tial formation before the nuclear membrane has disappeared 

 precludes its arising entirely from the substance of the germ- 

 nuclei, as maintained by Wilson ('95) for the segmentation 

 spindle in the sea-urchin's ^%g, and by Carnoy and Lebrun 

 ('97) for the egg of Ascaris. 



