The Development of the Animal World 65 



generations. This is the gist of the controversy con- 

 nected with the name of Weismann, but the elaborate 

 details of his system must be read in his works. 



Weismann h a thorough Darwinian. The characteris- 

 tic point of Darwin's work was to show the action of 

 the insufficiency of food, the consequent struggle for 

 life, and the selection (or survival) of the fittest or best- 

 equipped in the struggle. This Weismann fully accepts, 

 and adds an explanation of the cause of variations 

 which Darwin had not discussed. So far the essential 

 principles of Darwin's work remain, and it is absurd to 

 speak of them as abandoned. 



From another quarter, however, an important detail 

 of Darwin's theory has been called in question, and this 

 is the la3t general issue we need raise here. Darwin 

 clearly supposed that a new organ or a new species of 

 animal was evolved very gradually. Only slight changes 

 or improvements occurred in each generation, and it 

 would normally take thousands of generations to evolve a 

 new species. This seemed to be quite in accord with 

 the course of nature, in view of the comparative fixity of 

 species within historic times. But it has lately been 

 discovered that new species may be formed quite rapidly 

 and suddenly. An artificial interference with the 

 coupling of the germs may give rise to an organism with 

 such distinct characters as to constitute a new species. 

 An Austrian abbot, Mendel, found this by experiments 

 on plants years ago, and the distinguished Dutch 

 botanist, Hugo de Vries, has extended them, and now 

 has many supporters of his system of Mendelism or 

 Mutationism — the theory that new species were largely 

 sudden formations. 



These are the bare outlines of the theories that must 

 be borne in mind in considering evolution, and it 

 will be only proper in this work to avoid positions 



