THE WONDERS OF LIFE 



genetic and the other restrictively negative and ceno- 

 genetic. Palingenesis reproduces a part of the original 

 history of the stem; cenogenesis disturbs or alters this 

 picture in consequence of subsequent modifications of 

 the original course of development. This distinction is 

 most important, and cannot be too often repeated in 

 view of the persistent misunderstanding of my oppo- 

 nents. It is overlooked by those who (like Plate and 

 Steinmann) grant it only a partial validity, and by those 

 who reject it altogether (like Keibel and Hensen). The 

 embryologist Keibel is the most curious of these, as he 

 has himself afEorded a good rcia-ay proofs of the biogenetic 

 law in his careful descriptive-embryological works. But 

 he has so little mastered it that he has never under- 

 stood the distinction between palingenesis and ceno- 

 genesis. 



It is especially unfortunate that one of our most dis- 

 tinguished embryologists, Oscar Hertwig, of Berlin, who 

 provided a good deal of evidence in favor of the bioge- 

 netic law thirty years ago, has lately joined the opponents 

 of it. His supposed "correction" or modification of it 

 is, as Keibel has rightly said, a complete abandonment 

 of it. Heinrich Schmidt has partly explained the causes 

 of this change in his work on the biogenetic law. They 

 are not unconnected with the psychological metamor- 

 phosis which Oscar Hertwig has undergone at Berlin. 

 In the discourse on "The Development of Biology in 

 the Nineteenth Century," which he delivered at the scien- 

 tific congress at Aachen in 1900, he openly accepted the 

 dualist principles of vitalism (although he says they are 

 "just as unreliable as the chemico-physical conception 

 of the opposing mechanical school"). The views which 

 he has lately advanced on the worthlessness of Darwin- 

 ism and the unreliability of phylogenetic hypotheses, 

 are diametrically opposed to the opinions he represented 

 at Jena twenty-five years ago, and to those which bis 



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