58 FRANK R. LILLIE. 



globules in the yolk hemisphere is rarer than their formation in the 

 hyaline hemisphere, and was inclined to regard this as evidence 

 that there was a tendency for the eggs to orient themselves in 

 the centrifuge with the vegetative pole away from the center. 

 But I no longer believe that this is the case. The relative rarity 

 of maturation at the distal pole of centrifuged eggs must be due 

 to a different cause, and this is the great resistance of the yolk 



S&&S&& 



FIG. 2. Egg of C/^r/(?//d > /'Mj centrifuged 2, 300 revolutions in one minute at a radius 

 of 13 cm., 3 : 57 P. M., June 27, 1906 ; fertilized 3 : 58 P. M., killed 4 : 27 P. M. 

 The formation of the polar globules has taken place at the distal pole. The matura- 

 tion spindle migrated through the entire yolk -mass in the distal hemisphere to reach 

 this position. The sperm-nucleus surrounded by radiations is seen a short distance 

 above the egg-nucleus. The vacuolated area above is the gray cap. c.p. , central 

 pole (secondary axis) ; d.p. , distal pole (secondary axis). 



mass to penetration by the spindle. This conclusion is clearly 

 demonstrated by study of series of sections of eggs preserved at 

 regular intervals after centrifuging and fertilizing, which show 

 that many such eggs fail to form the polar bodies at all, or are 

 much delayed, or undergo their maturation divisions within the 



egg- 



