ROBERT CHAMBERS 37 



egg. The egg nucleus lies close to or within this area. Gradually 

 rays begin to appear in the jellying cytoplasm about the area. These 

 rays become more numerous and more pronounced until the entire 

 egg is occupied by a large monaster which corresponds exactly with 

 the fully developed sperm aster of a normally inseminated egg. 

 From now on the process is entirely analogous to that of a sperm ferti- 

 lized egg. During the development of the aster the hyaline central 

 area increases in size and the microdissection needle shows it to be 

 a liquid area characteristic of that of the sperm aster. When the 

 monaster disappears the liquid central area flows around the nucleus 

 now undergoing mitosis and accumulates at the two poles of the nu- 

 cleus into two polar areas. A jellying process now sets in with these 

 two areas as centers and results in the amphiaster preparator}-^ to 

 the first cleavage of the egg. 



In the mode of aster formation the only difference between the 

 sperm fertilized and the parthenogenetic egg consists in the manner 

 in which a liquid separates out of the jellying protoplasm in connec- 

 tion with the formation of the preliminary single aster. In the 

 fertilized egg radiations appear immediately about the sperm-head 

 and the accumulation of the liquid substance is from the beginning 

 through the agency of the ray-like channels of the growing aster. 

 In the parthenogenetic egg several vacuoles first appear in the cyto- 

 plasm. These vacuoles collect in the center of the egg after which 

 an aster appears. 



The frequent irregularities which obtain in parthenogenetic eggs 

 are apparently due to an incomplete fusing of the vacuoles and to 

 a lack of polarity in the preliminary stages of the aster formation. 

 In undertreatment, or when butyric acid alone is used, a monaster 

 developes as usual. Upon the disappearance of the monaster, the 

 persisting liquid centrosphere, instead of flowing to the two polar 

 regions of the nucleus, remains a single body. With the return of 

 the jellying period a single aster again forms and more fluid accumu- 

 lates in the centrosphere which increases in size. This process 

 repeats itself several times and segmentation of the egg never occurs. 



Eggs treated with butyric followed by a prolonged treatment of 

 the hypertonic solution become abnormal. In cases of this kind 

 the eggs, when returned to sea water from the hypertonic solution. 



