vi] RELATION TO MATTER 147 



in Stentor, and in Sycon 1 : indeed, as I have said, it 

 really seems to be an original attribute of life, only 

 more wonderful and startling than ordinary embryonic 

 development because it is no regular part of the cycle 

 of the species. Through its help the animal can extri- 

 cate itself from positions in which it has never before 

 been. 



But, like most other primitive attributes of life, it 

 has undergone considerable restrictions in the course 

 of evolution. Animals, like men, cannot have their 

 cakes and eat them. Three main factors have led 

 to a restriction of this power of regeneration. The 

 first is the formation of different substances for the 

 performances of different functions, and their subse- 

 quent segregation into different regions of the body. 

 These substances may get so specialized, so different 

 from each other and from their common ancestor, 

 that one cannot produce the other, and the presence 

 of both is necessary in a mass of substance which is 

 to give rise to a whole individual. In Stentor, for 

 instance, although both nucleus and cytoplasm alike 

 are living Stentor-protoplasm, yet a bit of one with- 

 out the other will not regenerate. Here the two 

 substances have been segregated by internal differ- 

 entiation within the cell. Something similar occurs 

 in Sycon, where the collar-cells by themselves cannot 

 regenerate the other forms of tissue necessary to make 



1 pp. 46, 47 and 94 respectively. 



102 



