DU BOIS-REYMOND. 1 67 



is in actual process of evolution. He overlooked the obvious 

 consideration that even the consciousness of the human race 

 must have arisen gradually by evolution through many 

 phylogenetic stages precisely in the same way that even yet 

 the individual consciousness of every child is gradually 

 completed in the course of many ontogenetic stages. 



Again, this same want of insight into the functions and 

 the physiological process of evolution accounts for the fact 

 that even at the present day esteemed and learned natural- 

 ists are earnestly discussing the question whether the 

 creation of species, or, in other words, the phyletic evolution 

 of forms, took place suddenly or gradually. This dispute 

 is as irrational as would be a dispute as to whether the 

 mouse is a great or a small animal. The elephant will of 

 course declare the mouse to be a tiny creature, while the 

 louse, living on the skin of the mouse, must regard the 

 latter as an animal of gigantic size. Just as in the one case 

 the estimate of extension in space is purely relative, and only 

 to be taken in a relative sense, so in the other case is the 

 estimate of extension in time. 



Every process of evolution as such is always continuous, 

 and real leaps or interruptions never occur. Natura non 

 facit saltus — nature never leaps. This is true both of on- 

 togenetic and of phylogenetic processes : of the evolution 

 of the individual as well as of that of the species. It is 

 true that in Ontogeny leaps sometimes appear to occur, 

 e.g. when the butterfly is developed from the pupa into 

 which the caterpillar has been transformed, or when a 

 Medusa is developed from an entirely dissimilar hydra-form 

 Polyp. But the morphologist who step by step studies the 

 exact course of these processes of evolution, finds that, 



