DURATION OF SPECIES. 351 



species ; but these have only anticipated their fate, 

 for M. Naudin contends that most of the extinct 

 species have died a natural death from exhaustion of 

 force, and that all the survivors are on the way to it. 

 The great timepiece of Kature was wound up at the 

 beginning, and is running down. In the earlier 

 stages of great plasticity and exuberant power, diver- 

 ' sification took place freely, but only in definite lines, 

 and species and types multiplied. As the power of 

 survival is inherently limited, still more the power of 

 change : this diminishes in time, if we rightly appre- 

 hend the idea, partly through the waning of vital 

 force, partly through the fixity acquired by heredity 

 like producing like, the more certainly in propor- 

 tion to the length and continuity of the ancestral 

 chain. And so the small variations of species which 

 we behold are the feeble remnants of the pristine 

 plasticity and an exhausted force. 1 This force of 

 variation or origination of forms has acted rhythmi- 

 cally or intermittently, because each movement was 

 the result of the rupture of an equilibrium, the liber- 



1 In noticing M. Naudiu's paper in the Compte* Jlendus, now re- 

 printed in the " Annales des Sciences Naturelles," entitled " Variation 

 desordonnee des Plantes Hybrides et Deductions qu'on peut en tirer," 

 we were at a loss to conceive why he attributed all present variation of 

 species to atavism, i. e., to the reappearance of ancestral characters 

 (American Journal of Science, February, 1876). His anterior paper 

 was not then known to us ; from which it now appears that this view 

 comes in as a part of the hypothesis of extreme plasticity and variabil- 

 ity at the first, subsiding at length into entire fixity and persistence of 

 character. According to which, it is assumed that the species of our 

 time have lost all power of original variation, but can still reproduce 

 some old ones some reminiscences, as it were, of youthful vagaries 

 in the way of atavism. 



