148 



CHAS. B. WILSON. 



angles to the plane of cleavage^ and since the first three 

 planes are in the three dimensions of space the successive 

 elongations restore the sphericity of the egg. During the 

 flattening together at the close of the third segmentation 

 there is a twisting to one side^ whereby the four upper 

 blastomeres come to lie over the grooves between the lower 

 four, i.e. the cleavage is spiral (fig. 54). 



A change now takes place in the relative activity of the 

 polar bodies ; the first one has been more active hitherto, but 

 it now loses its marked polarity and begins to resume its ori- 

 ginal spherical form. One of its poles has already been re- 

 placed by a bunch of radiating filose threads, and the other 

 one now disappears gradually until the only remaining signs 

 of activity are occasional spinnings from various points on 

 the surface. 



The second body, on the contrary, increases in activity; 

 the processes at either end enlarge, and the filose spinning 

 increases proportionally. The band of protoplasm connecting 

 it with the egg changes continually in size and contour, and 

 occasionally a lump or swelling appears near the centre of 

 this band, looking like a third polar body. But it soon dis- 

 appears. The two figures given (44, 45) show the relative 

 activities in late stages of cleavage, and they also show that 

 the chromatic substance is affected by these activities. 



In the first figure the chromatin appears in the form of 

 grains scattered through the body; in the second figure it has 

 been gathered into a nuclear-like mass near the centre, whose 

 size and shape change under the influence of the spinning. 



This change of the chromatic substance under the influence 

 of filose activity in the polar bodies corresponds well with the 

 changes in position, size, and shape of the chromosomes in 

 the nucleus during karyokinesis under the influence of the 

 spindle activities, and is another evidence of the close rela- 

 tion between the two. We have no means of knowing how 

 far they may agree in detail, but they are worthy of note as 

 showing that the filose activities have a tendency in the 

 same direction as those of the segmentation spindle. 



