THE BEGINNINGS OF LIFE. 637 



undergo a direct process of development., we first begin 

 to obtain such regularly-recurring and definite assem- 

 blages of animal and vegetal forms as are usually 

 grouped under the name of c species.' 



These c species' are represented either by solitary 

 hermaphrodite individuals, by two sexually -distinct 

 individuals, or by a series of transitional and deri- 

 vative individuals of which all the earlier forms are 

 sexless and still retain the power of undergoing pro- 

 cesses of asexual multiplication, although in the last 

 form fecundated germs are produced by a true sexual 

 process. 



Such organisms have gradually become more highly 

 organized than the c ephemeromorphs,' and they are to a 

 corresponding extent less immediately capable of being 

 influenced by changes in their environment or other 

 modifying influences. Moreover, as soon as sexual 

 reproduction is initiated and homogenesis becomes the 

 rule, the c laws of heredity ' come into action, and 

 an internal conservative principle begins more and 

 more to take root. 



The processes comprehended under what Mr. Darwin 

 has termed c Natural Selection,' being essentially based 

 upon these laws of heredity, can only come into play 

 as an originator of specific transmutations amongst 

 such forms of life as habitually reproduce by a process 

 of homogenesis. It can only begin to be influential, 

 therefore, when we have passed beyond the limits of 

 that vast and intricately interrelated assemblage of 



