322 EDWIN G. CONKLIN 



the vegetal pole (fig. 21), but however far it may be from the 

 animal pole it moves back to its normal position to finish its 

 division unless it is prevented by very long or strong centrifu- 

 ging; in the latter case the polar body may be cut off wherever the 

 spindle happens to be. Thus in eggs which are centrifuged from 

 30 minutes to 2 hours during the maturation divisions the polar 

 bodies may be extruded at any point on the surface. 



3. Formation of giant polar bodies (figs. 23 to 27, 31 to 58) 



Most polar bodies that are formed during centrifuging and all 

 that are formed at a distance from the animal pole are larger 

 than normal ones, though they may vary greatly in size (figs. 

 32 to 58). The size of a polar body or of any cleavage cell 

 depends upon the position of the mitotic figure at the time of cell 

 constriction, since the partition wall between daughter cells 

 always goes through the equator of the spindle; when one pole 

 of the spindle is pressed against the cell membrane, as in the 

 maturation divisions, the size of the polar body depends upon 

 the length of the spindle. The extremely small size of normal 

 polar bodies is due to the fact that the maturation spindle con- 

 tinually grows shorter during the later stages of mitosis, and 

 whenever giant polar bodies are formed it is due to the median 

 position of the spindle in the cell or to its elongation if it is 

 attached to one pole. 



When centrifuging occurs during the anaphase of a matura- 

 tion division after the peripheral pole of the spindle is closely 

 attached to the surface of the egg at the animal pole the spindle 

 may become much elongated, especially if yolk is driven to that 

 pole (figs. 6, 22 to 26). And conversely, whenever there is a 

 stretching of the spindle, it is evident that one or both of the 

 poles are attached to the surface layer even though this at- 

 tachment may not be directly visible. Consequently, the elonga- 

 tion of the spindle in the formation of giant polar bodies in- 

 dicates that one pole of the spindle is attached to the surface at 

 the animal pole. The fact that a polar body may be given off 

 at the opposite pole of the spindle, i.e., at the vegetal pole of 

 the egg, and yet the polarity of the egg remain undisturbed and 



