266 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



the Darwinian school, to regard the efficient cause 

 of the changes in beings in the struggle for life 

 leading to a natural selection with survival of the 

 fittest ? Is it expedient to listen to more mysterious 

 and obscure causes, such as the theory of Weismann 

 on the continuity of the germ-plasm, transmitted 

 by parents with special qualities which selection 

 afterwards develops, or to the hypothesis of Naegeli 

 on a natural and permanent tendency in each in- 

 dividual towards a more perfect state, a tendency 

 which added to Darwinian selection determines the 

 evolution of morphological characters ? Carried 

 into this field, the question of the origin of species 

 is raised to a problem of sublime biological philo- 

 sophy, the discussion of which is still open, and 

 an agreement upon which among naturalists is not 

 on the eve of conclusion. 



What we may affirm is that the too exclusive 

 Darwinian theory of the struggle for life has been 

 subjected for the last quarter of a century to a 

 bombardment of serious objections, which have 

 made it lose much ground. Brown and A. Braun 

 have pointed out the uselessness of many organs 

 which, on the hypothesis of selection, could neither 

 have been produced nor modified. H. Spencer has 

 shown that very slight variations could neither be 

 of use to the individual nor afterwards be adopted 

 by selection. Finally, Dollo and Rosa have proved 

 in recent years that the variation of groups is 

 not indefinite, as required by Darwin's theory, 

 but, on the contrary, limited by a duration of time 

 varying according to the groups. 



It appears that the majority of modem naturalists 



