THEORY OF THE GERM-PLASM 425 



the non-mosaic theory denying qualitative division and em- 

 phasising the importance of environmental interaction in the 

 widest sense. 



It must be carefully noted that as far as the eye can see, 

 there is in the development of the embryo only one kind of cell- 

 division, which involves a visibly accurate longitudinal halving 

 of each of the chromosomes of the nucleus. Therefore if there 

 is any qualitative or differential division it must be of a subtler 

 sort. 



§ 2. Weismann's Theory of the Germ-plasm 



No one has done more to further the scientific study of here- 

 dity than Prof. August Weismann, of Freiburg, although his 

 work has been on different lines from that of the statistical 

 school which we particularly associate with the names of Mr. 

 Francis Galton and Prof. Karl Pearson, or from that of the 

 experimental school which we particularly associate with the 

 names of Gregor Mendel and Mr. Bateson. In general we 

 may say that Weismann has thought out a theory of heredity, 

 coherent with a theory of development and a theory of evolution, 

 which has inspired much research and has commanded the 

 admiration of his most resolute opponents. He has done for 

 the study of heredity what Dalton with his atomic theory 

 did for chemistry, and though his theory will doubtless be 

 developed, as Dalton's has been, it seems unlikely that the 

 fundamental ideas of Weismannism will be discredited in the 

 future evolution of biology. 



As Weismann's interpretations have gone on growing as 

 facts accumulated and as his insight increased, they present 

 difficulty to those who have not followed their development, 

 and it is therefore necessary to present a brief statement of 

 Weismannism as developed, for instance, in The Evolution 

 Theory (1904). 



