50 Heredity and Social Progress 



naturally arises whether it is a phenomenon of 

 reproduction alone or whether this formation 

 may not be a general characteristic of cell 

 division. The ease with which the stages in- 

 cident to reproduction may be observed, the 

 simplicity of the conditions, and the interest 

 in the problem naturally make it a starting- 

 point of these investigations. But what is 

 here true, may also be true of other forms of 

 cell division. Two facts appear that seem to 

 have a general significance. In the first place, 

 the specialization or transformation due to the 

 retention of the egg in the mother organism 

 can be thrown off and the egg brought back 

 to its original state. This is the reason for 

 the emission of the first polar body. 1 In the 

 second place, there can be an actual division 

 of the egg so that it loses some of the parts 

 necessary for a complete existence. The claim 

 has been made that the egg loses its centro- 

 some by the emission of the second polar 

 body, and that the replacement of this neces- 

 sary part is made possible by the union with 

 the male germ. A polar body would then be 



1 Weismann, "Essays on Heredity," p. 351. 



