ROBERT CHAMBERS 39 



only two focal points the liquid collects into two bodies, a typical 

 amphiaster then develops, and the egg cleaves into two normal 

 blastomeres. 



Aster formation not only consists in a jellying process but also in 

 the separating out of a liquid. The optically visible phenomenon 

 peculiar to the parthenogenetic egg consists in the manner in which 

 this liquid begins to separate out of the egg cytoplasm preparatory to 

 the formation of the preliminary single aster. In the sperm fertilized 

 egg both processes are rapid and occur together, radiations appear 

 immediately about the sperm-head, and the accumulation of the 

 liquid substance is from the very start through the agency of the 

 ray-like channels of the growing aster. In the parthenogenetic egg 

 the jellying process is apparently very slow, and the separating out 

 of a liquid takes place before the cytoplasm is stiff enough to exhibit 

 channels through which the liquid flows to the center. The liquid 

 first collects into several vacuoles and an optimum treatment is nec- 

 essary to cause these vacuoles to fuse into one body with the subse- 

 quent formation of a single aster. Overtreatment causes the appear- 

 ance of many vacuoles scattered throughout the egg resulting in 

 multiple asters. Undertreatment may result in the formation of a 

 single aster which, however, periodically disappears and reappears as 

 a single aster. 



The parthenogenetic treatment, in order to be successful, must 

 not only bring about the separating out of a liquid from the egg 

 cytoplasm, but must also induce polarity within the resulting hyaline 

 area in order to enable it to form two centers about which an amphi- 

 aster may develop. 



