APPENDIX. 175 



upon the nature of the germ plasm. To him it con- 

 sists of ultimate living particles, to which he assigns 

 various and specific purposes, and groups them at 

 will, group within group, like nests of Chinese boxes. 

 The biophores (his conceived units) have the capacity 

 of growth and reproduction a generous concession 

 indeed. They are groups of chemical molecules, far 

 beyond the highest powers of the microscope, and 

 cannot therefore be investigated by our senses ; they 

 are conceptions, not perceptions. These biophores 

 are arranged in groups, called determinants, one for 

 every part of the adult which is capable of variation ; 

 groups of determinants are termed " ids," and groups 

 of ids are termed " idants," the last being visible in 

 the ovum as a brightly-stained rod of unclear 

 matter. By the multiplication, differentiation, and 

 disintegration of these various groups, the adult body 

 is formed, and Weismann is prepared to explain 

 every step. 



Speaking in I883 1 of Darwin's theory of pan- 

 genesis, Weismann remarks : " We become lost in 

 unfounded hypotheses." I think this is a true and 

 allowable criticism, but I also think that it applies in 

 far greater measure to the theory of the germ plasm 

 developed by Weismann himself. It may be pointed 

 out that Darwin placed little store upon his theory, 

 and apologised for its speculative nature, not only in 

 the letters already referred to, but in his work upon 

 "The Variations of Plants and Animals under 

 Domestication," where it appears in a single chapter 



1 Lecture on Heredity, op. tit.) p. 77. 



