320 EDWIN G. CONKLIN 



were then allowed to stand for one and one-half hours before 

 thej^ were fixed, during which time the spindles advanced to the 

 anaphase. In these four figures the spindles he near the middle 

 of the egg and the egg contents are not regularly stratified but the 

 spindles and some of the cytoplasm project into the yolk in such 

 a manner as to suggest either that the spindles were limited in 

 their movement at the time of centrifuging or that after centri- 

 fuging they were moving back to their original positions. In 

 either case it seems necessary to assume that the connection of 

 the spindles with the animal pole, probably by means of proto- 

 plasmic fibers, was never lost. Finally such spindles probably 

 come to the surface of the egg at the animal pole and form nor- 

 mal polar bodies since in all eggs of this experiment which were 

 allowed to develop further the polar bodies are typical in ap- 

 pearance and position, lying at the center of the ectodermal 

 pole. 



Figures 13-18 represent eggs which were centrifuged in the 

 late anaphase of the first maturation division after the spindle 

 was closely attached to the animal pole; in figure 13 the egg was 

 fixed immediately after centrifuging; in figures 14 to 18 they 

 were left in normal conditions for one and one-half hours be- 

 fore being fixed. In every case the spindle has remained in its 

 original position and a normal polar body has been formed, 

 though the cytoplasm and yolk are abnormal in position. As 

 in previous figures the sperm nuclei show little indication of 

 having been moved by the centrifuging. In figures 17 and 18 

 the lane of cytoplasm leading from the animal pole to the cyto- 

 plasmic field indicates either that the egg substances were not 

 regularly stratified by centrifuging, or that they are beginning 

 to return to their original positions. 



If the first maturation division occurs normally it is always easy 

 thereafter to identify the original animal pole of the egg, how- 

 ever much the egg substances may have been moved out of their 

 normal positions, by the location of the first polar body. This 

 is an invaluable landmark since as long as the polar body re- 

 mains attached to the egg it does not move from the position at 

 which it was first formed. Before the formation of the first polar 



