DE VEIES'S THEORY OF MUTATIONS. 205 



HUGO DE VKIES'S THEORY OF MUTATIONS.* 



By Professok A. A. \V. HUBRECHT, 



UNIVERSITY OF I'TKECHT. 



r I ^HE theory of evolution has influenced human thought in the most 

 -*- various ways during the past half century. In the sphere of 

 biological science, where Darwin sowed the seeds which have grown up 

 with such unexpected luxuriance, there has been a continuous process 

 of fermentation which shows no signs of subsiding. 



Still it has often seemed as if the immense mass of facts, which 

 Darwin collected and arranged with so much care and skill, were pro- 

 visionally looked upon as sufficient, and as if actual experiment were 

 no longer a primary necessity. Whenever a new observation happened 

 to be made, it was in danger of being drowned in pailfuls of theoretical 

 considerations. Genealogical trees were planted, grafted, transplanted 

 and finally often committed to the flames. Statistics were brought 

 together to demonstrate the importance of natural selection, not only 

 in the struggle between individual organisms, but also within the 

 organism between the elements of which it was composed. Thus Eoux 

 wrote in 1881 his 'Kampf der Theile im Organismus,' Weismann only 

 a few years ago (1896) his 'Germinal Selection.' In a series of very 

 remarkable publications the Freiburg professor of zoology has thrown 

 light on a series of difficult problems and has shown himself to be not 

 only a faithful pupil of Darwin, but one who on several occasions has 

 been more ultra-Darwinian than perhaps Darwin himself would have 

 been. 



Those who consult the very voluminous literature of the subject will 

 soon be convinced that the number of biologists who have preferred 

 patient experimentation to theoretical speculation is very limited indeed. 

 Experimentation on this subject demands a great deal of time, of 

 patience, of devotion, and is liable to meet with many pitfalls. Yet 

 for those who came after Darwin this should have been the task that 

 lay closest to their heart : to test the two great groups of facts on which 

 descent and selection are founded, by means of new and more detailed 

 experiments. 



These two groups of facts are the phenomena cf heredity and of 



* This article was written in English by Professor Hubrecht, the eminent 

 Dutch zoologist, who has an equal command of the French and German lan- 

 guages. Professor de Vries is at present in the United States in order to 

 lecture at the University of California and other institutions. — Editor. 



