142 



CHAS. B. WILSON. 



second body is pulled out at right angles to that surface, until 

 sometimes the perpendicular axis becomes the longer one. 

 Evidently its attachment must be firm enough to bring about 

 such a change. 



Its spinning activities are not disturbed in the least, and 

 the former poles remain the centres of such activities. This 

 often results in an irregular quadripolar appearance, the two 

 connecting bands of protoplasm arising from the vertical 

 poles, while from the horizontal ones radiate long filose spin- 

 threads. 



We have said that the cleavage groove nearest the polar 

 bodies usually occupies two thirds or more of the entire 

 diameter of the egg. Hence, if the polar bodies remained 

 as near the bottom of the groove as they were when it started, 

 they would be drawn in at least to the centre of the egg. 

 But such is not the case. They do sometimes enter within 

 the general contour of the whole mass, but they usually 

 follow the groove only a little way, and remain partially or 

 wholly outside the general contour. As a result, the band of 

 protoplasm connecting the second body with the egg appa- 

 rently changes its point of attachment to the latter. Instead 

 of remaining near the bottom of the groove, it removes to a 

 comparatively long distance from it on the side of one of 

 the blastomeres (fig. 46). 



Is this change of position real or apparent ? Is it the 

 body which has changed, or the bottom of the groove ? 



That portion of the egg where the connecting band origin- 

 ally appears is the centre of activity during the extrusion of 

 the bodies, and naturally remains connected with them during 

 their filose spinning. It then becomes the point at which the 

 protoplasmic activities resulting in the first cleavage are 

 manifested. Hence, if the point of attachment were to be 

 changed, it would seem natural that it should be toward some 

 other centre of activity. But no such centre can be found at 

 or near the surface of either blastomere, so that a priori we 

 should not expect any change. Again, the only way in 

 which such a connecting band could change its position would 



