THE BEGINNINGS OF LIFE. 261 



which I think have never been represented. It was 

 quite a new world/ Ehrenberg was convinced that 

 twelve species described by O. F. Miiller as belonging 

 to the genus Vcrtuella^ were only different modifications 

 of one and the same species. And yet these twelve 

 forms were so different that Lamarck and Bory de 

 Saint -Vincent ranged them under several different 

 genera. 



Again, although much uncertainty still prevails as to 

 the extent of modification which the Ciliated Infu- 

 soria may undergo, and as to the reality of some of 

 the marvellous metamorphoses that have been alleged 

 to occur, still the almost innumerable variations in 

 their modes of reproduction \ are quite in accordance 

 with such alleged modifiability. The absence in them 

 of any hereditary tendency to develop in a given direc- 

 tion or after a definite fashion, should render such 

 organisms extremely liable to change throughout their 

 whole life. Having no constant tendency to assume 

 any given form, and possessing an extremely simple 

 organization, there is an absence of the usual conserva- 

 tive influence which opposes the occurrence of internal 

 changes and resists the modifying agency of altered 

 external conditions. The forms, therefore, which such 

 organisms may assume during their growth may be 

 expected to vary in a most marked manner from time 

 to time. And this also is a well-known and thoroughly 



1 See Appendix E, pp. xcvii-cv. 



