14# THE THEORIES OF EVOLUTION 



and can therefore reproduce the whole series? The 

 problem is solved by the theory of the continuity of 

 the germ plasm. 



When the ovum undergoes cleavage, the sum total 

 of its determinants is divided into two, then into four, 

 then into eight unequal sums, but the totality of the 

 germ plasm is not destroyed by the heterogeneous 

 cleavage which produces the successive idioplasms; at 

 every cleavage, a minute particle of germ plasm re- 

 mains unaltered in one of the two blastomeres while 

 the other blastomere and all its descendants w 7 ill never 

 contain any. This particle of unaltered germ plasm 

 is transmitted from cell to cell until it reaches the cell 

 destined to form the sexual elements. This mother- 

 cell then produces through homogeneous cleavage the 

 many sexual cells of the new individual and every one 

 of the blastomeres receives a minute particle of the 

 parental germ plasm thus transmitted through all 

 segmentations. 



In this w T ay the organism is divided up into two 

 independent parts: the differentiated tissues which 

 constitute the soma and cannot revert to the undiffer- 

 entiated state of germ cells, and the sexual ele- 

 ments or germina which have received the parent's 

 germ plasm in its original condition and are still able 

 to initiate a new development. 



This process continues from generation to genera- 

 tion and the result is that every individual contains in 



