BLACKMAN-. THE SPERMATOGENESIS OF SCOLOPENDRA. 53 



In the metaphase the astral fibres found in the equatorial region are 

 very much more numerous than elsewhere and are much better de- 

 veloped. Their place of attachment upon the cell membrane is confined 

 to a rather limited zone about one third the cell diameter in width. 

 During the subsequent lengthening of the cell in the anaphase this area 

 at first remains practically the same, but later as the elongation proceeds 

 becomes still more restricted to probably one half of its former width. 

 Thus, at the time of the constriction of the cell membrane, the attach- 

 ment of the greater number of the astral rays is confined to the small 

 area of the cell wall with which this process is chiefly concerned, i. e. 

 the equatorial portion only. Those which are attached to the cell wall 

 at the points between this area and the poles of the cell, are very few 

 and very faintly developed ; furthermore they are so arranged that, 

 practically, they can exert by their contraction no considerable force 

 upon the cell membrane. This is owing to the fact that as the cell 

 lengthens the polar regions become cone-shaped, and the centrosome, 

 being at the apex of this cone, the force exerted by the contraction of 

 these rays acts approximately parallel to the cell membrane, so that it 

 can have no appreciable constricting effect upon this structure. With 

 the aid of the polar astral rays and the central spindle, however, these 

 fibres serve more firmly to anchor the centrosomes. Soon these fibres, 

 being no longer of any use, disappear and are seen no more. 



In a slightly later stage (Fig. 68), when the cell wall has begun to 

 show signs of constriction in the equatorial region, the centrosome again 

 changes its position with regard to the cell membrane, as already de- 

 scribed. The cell wall at the point of contact with the centrosome is 

 drawn inward, thus causing a considerable depression in this region 

 (Fig. GO). 1 This depression shows that the centrosome is attached to 

 the wall at the poles, and that the force necessary to complete cell 

 division is obtained, not by the divergence of the centrosomes, as was 

 apparently the case in the separation of the chromosomes, but by a force 

 exerted through the astral fibres. 



Now a few words in regard to the significance of these phenomena. 

 I have noted above that during the metaphase the astral rays which, 

 extending through the cytoplasm, envelop the spindle on all sides, 

 plainly come in contact with the cell wall and very probably are attached 

 to it. That these rays, which are by far the most numerous and best 

 developed of those constituting the asters, should do this to no purpose, is 



1 The same appearance is also noticed, though to a less extent, in the first sperma- 

 tocyte of the larger cells (Plate 3, Figs. 37, 38). 



