The Development of the Frog 15 



In the case of the tissue cells of the higher 

 organisms there is no method of removing this 

 substance, so that these cells must eventually 

 perish ; but in the case of the simplest uni- 

 cellular organisms, and in the reproductive 

 cells of the higher forms, this substance is 

 removed in a single operation, and the cell 

 thus enabled to begin a new series of di- 

 visions. 



Labbe found among certain insects a reduc- 

 tion of chromatin, not followed by fecundation, 

 that was followed by cell division and develop- 

 ment ; and other cases of parthenogenesis are 

 known. 



The expulsion of chromatic material is rep- 

 resented in higher organisms by the extrusion 

 of the first polar body, and " if one could 

 prevent the extrusion of the second polar 

 body, all beings would develop parthenogen- 

 etically." 



The formation of the second polar body 

 reduces the amount of chromatin and the num- 

 ber of chromosomes, and makes impossible 

 further development, until fresh chromatic 

 material has been added by the process of 

 fecundation. 



It will be seen from the above examples 



