6 PRINCIPLES OF BREEDING 



body ; that the gemmules are aggregated in the reproductive 

 cells ; and that by this means the characters of the original 

 structure are transmitted from generation to generation. 



Professor Weismann, 1 elaborating the theory of the 

 continuity of germ-plasm, advanced by Francis Galton, 

 maintains that there are two distinct classes of cells in- 

 volved in the structure of the reproductive germ-cells, 

 the one being the origin of the body, or soma, the other 

 being exclusively for the development of reproductive 

 germ-cells, which, though associated with the body, are 

 nevertheless, in everything, except in the matter of protec- 

 tion and nourishment, independent of it. The reproductive 

 germ-plasm in any germ-cell is therefore supposed to be 

 derived from the parent germ-cell, and not from the in- 

 dividual in which it was produced. This theory practically 

 excludes the possibility of the continuance in a breed of 

 the results of any change arising in the individual that 

 does not originate in the cells exclusively devoted to the 

 perpetuation of the species. Any change in, or influence 

 exerted upon, the body of the immediate parent could 

 not, according to Weismann, be reproduced in the young. 

 Although we are not in a position actually to disprove 

 this theory, which has made the name of Weismann familiar, 

 we are not prepared to accept it as indisputable. 



G. Archdall Reid in The Principles of Heredity assumes 

 that "educated men are agreed that all forms of life are 

 related to one another through an ancestry which, in the case 

 of more divergent forms, is very remote ; and that all the 

 higher and more complex forms have been evolved from 

 lower and more simple forms." He divides all acquired 

 characters that appear in the process of evolution or other- 

 wise into two groups : (a) " inborn traits or characters, those 

 which take origin in the germ-plasm," and give rise to 

 " variations," or " new inborn characters," which are congenital 

 and come to the individual " by nature " ; and (If) " acquired 

 characters or modifications of inborn characters, caused by the 

 play of forces from the environment on those characters after 

 (as a rule) they have developed from the germ-cell. The 

 importance of exact definition is due to the fact that, while it 



1 A translation of Weismann's Essays was published by the Clarendon 

 Press, Oxford, in 1889 (New edition, 1891-2), and one of his, The Germ- 

 Plasm : A Theory of Heredity, by Walter Scott, Limited, London and 

 Newcastle, in 1893. 



