BLACKMAN : THE SPERMATOGENESIS OF SCOLOPENDRA. 49 



The chromosomes of this small spindle are grouped together very 

 closel}', but their outlines remain distinct. In comparison with the size 

 of the cell, they are considerably larger than in the spermatocytes of the 

 large type, although in actual size they are smaller. They are ovoid or 

 beau-shaped and very seldom show the four-lobed form characteristic of 

 the earlier stages and of the tetrads of the large spermatocytes. 



Very soon after the chromosomes are drawn into position the centro- 

 somes move apart and the spindle lengthens until the cell presents the 

 appearance shown in Figures 65 and 158 (Plate 9). At this time the 

 cell resembles the ordinary male cell more than at any previous time, 

 although even now it presents several unusual features. The chromosomes 

 remain as in the stage last described except that they are not so crowded. 

 The cone-shaped areas of cytoplasm at the poles of the spindle are still 

 visible, but are less marked than formerly, owing to the fact that the 

 astral rays are better developed in these regions. However, they are 

 still very apparent. At this stage the fibrillar structures of the cell are 

 more conspicuous than at any time previously. It can be seen with the 

 greatest distinctness that the astral radiations near the equator cross each 

 other and proceeding on through the cytoplasm, come in contact with 

 the cell membrane, to which they probably attach themselves. These 

 astral rays, which stand forth with clear-cut outlines, are distinctly seen 

 to be branched near their distal ends. 



The centrosphere is a rather large, finely granular body which has the 

 form of a wedge or cone with the apex directed toward the equator of 

 the spindle. The centrosome within it is elongated in the same direction 

 and is also conical, although much more acute than the centrosphere. 



The next change which the cell undergoes is very unusual and I 

 believe has been reported only in Scolopendra heros (Blackman, :Ol). 

 The centrosomes continue to move in opposite directions until they reach 

 points only a short distance from the cell membrane. Here they come 

 to rest and retain their position until the separation of the chromosomes 

 during the anaphase. But the peculiarity about this movement is that 

 the mantle nbres still converge to the points occupied by the centrosomes 

 before the last part of their migration. From these points, which in my 

 preliminary paper I called the apical points, small bundles of fibres 

 extend to the centrosomes, thus preserving the connection between the 

 spindle and the dynamic centres of the cell. That the centrosomes have 

 not lost their function, is shown at this stage by the fact that the astral 

 rays still radiate from these bodies. As to what is the significance of 

 this marked modification of the mitotic figure, I will not venture a 



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