THEORY OF THE GERM-PLASM 429 



the non-mosaic theory denying quahtative division and em- 

 phasising the importance of environmental interaction in the 

 widest sense. 



As far as experiment goes, evidence can be adduced in favour 

 of both interpretations, and difficulties can be urged against 

 both ; the question comes to be — since both views are unverifi- 

 able, which gives the most complete and consistent formulation 

 of what we know to be facts ? In their extreme forms the two 

 theories are irreconcilable, but with some mutual concessions 

 it seems possible to combine them. 



§ 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, 

 ^vhich 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). 



