534 BULLETIN OF THE 



of the asters in cell division have often been represented, since the time 

 of Auerbach ('74, Taf. IV. Fig. 11), as being at certain stages curved, 

 but in none of them is the slight curvature of such a nature as to pre- 

 vent each ray from lying wholly in a plane. The rays of the spiral 

 asters are often much more prominently curved, and are not limited to 

 a single plane. But they also are not constant phenomena of any given 

 stage, nor of all asters. Therefore, whatever may be the cause of this 

 peculiar arrangement, it is not likely to be of fundamental importance. 

 The spiral condition will probably be instructive only in so far as it 

 throws light on the nature of asters in general, — on the physical state 

 of their rays. 



The spiral course of the rays in the superficial (polar-globule) aster 

 might fairly be accounted for by assuming that it is caused by the force 

 which urges the tip of the maturation spindle into contact with the 

 envelope of the egg. The spiral form of the external aster would, then, 

 be only one of the results of its being compelled to adjust itself to an 

 altered position. What in one case is effected by a simple outward and 

 backward deflection of the rays producing the funnel-shaped figure, may 

 in this case be accomplished or aided by a lateral deflection. The spiral 

 course would evidently allow the centre of an aster with rays of fixed 

 length to approach nearer the surface than could otherwise be. If 

 this is the correct explanation, the spiral, like the funnel, results from 

 the force which impels the archiamphiaster against the resisting enve- 

 lope of the yolk. In one case the adjustment is accomplished by a sim- 

 ple bending of the rays, each of which continues to lie wholly in a plane 

 coinciding with the axis of the spindle ; in the other case the same end 

 is attained by the addition of another curvature which takes the ray out 

 of that plane. 



This explanation would, I think, be entirely satisfactory if the phe- 

 nomena were limited to the superficial aster, but it is difficult to con- 

 ceive how a force (contraction 1), acting in any part of the yolk, could 

 induce such extensive spirals as are seen in the rays of the deep aster 

 of Fig 78. If the rays are the result of a constructive process, one 

 might assume that this construction advances in straight lines till it 

 reaches the periphery of the yolk, and that a deflection is then necessi- 

 tated on account of the resistance offered by the yolk envelope, — a resist- 

 ance that is sometimes overcome by the joint action of neighboring rays, 

 which thus cause pseudopodal elevations of the surface. This resist- 

 ance would then, it may be assumed, be propagated along the existing 

 portions of the ray, — such a transmission being rendered possible by 



