THE THEORY OF EVOLUTION 



ories of heredity and the constitution of the germ- 

 plasm, which have been remarkably confirmed by the 

 extensive studies which have grown out of the re- 

 searches in the exact mechanism of heredity made by 

 Mendel. Weismann was the first writer who strongly 

 questioned the hereditary transmission of charac- 

 teristics which had been acquired during the life- 

 time of the parent, maintaining that all new struc- 

 tures must first arise in the germ-plasm. He thus 

 rejected altogether the effects of the use and disuse 

 of organs, which Darwin had admitted and to which 

 Lamarck had attributed the primary role in the 

 work of transformation, and regarded natural selec- 

 tion alone as the all-important factor. It would 

 require far more time than is at our disposal to give 

 even an outline sketch of Weismann's theories and 

 it must suffice to point out that his views are still 

 largely in the ascendant and that the great number 

 of naturalists who constitute the so-called ''Neo- 

 Darwinian School' look upon Weismann as their 

 foremost spokesman. 



Palaeontologists, whose studies deal with the fossil 

 remains of the ancient plants and animals which 

 once inhabited the earth, but are now altogether ex- 

 tinct, have not, as a rule, been satisfied with the 

 theory of natural selection as an adequate explana- 

 tion of organic evolution. It was a palaeontologist, 

 von Waagen, who, in 1867, first pointed out a dis- 

 tinction, which may yet prove to be the first step 

 toward the formulation of an entirely acceptable 



