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advantageous endowments passed on to the next generation. 

 How this is brought about will appear if we remember that at 

 each sexual union there is a mixture of two reproductive elements, 

 and that each of these is the product of the fusion of two other 

 reproductive elements of the preceding generation. Thus it fol- 

 lows that the germinal elements of no one member of the species- 

 can ever be the same as that of any other member ; in fact, 

 each such germinal element has had a different ancestral history, 

 and each represents an admixture derived from thousands, and 

 perhaps millions, of individuals in different lines of descent. In 

 the union of any two of these enormously complex but always 

 differino- o-erminal elements we have the cause of innumerable 

 congenital variations — the only variations which Weismann will 

 allow are transmissible by heredity. Though we may thus make 

 a reasonable attempt to explain the raison d'etre of the process 

 of sexual reproduction, the cause which led to its adoption is a 

 problem which still awaits suggestion and solution. 



So far, then, Weismann leads us to the conclusion that the 

 dominion and influence of natural selection can only be made to 

 extend as far back as the Protozoa, over which it is unable to 

 exert any influence at all, for, if natural selection depends for its 

 activity upon the occurrence of congenital variations, and if con- 

 genital variations in their turn depend upon the exercise of the 

 exual method of reproduction, it follows that organisms which 

 do not propagate themselves by this method cannot present con- 

 genital variations, and cannot thus come under the dominion of 

 natural selection ; in other words, while for unicellular organisms 

 Weismann is an exclusive advocate of the views of Lamarck, 

 whose theory, as is well known, was mainly based upon the effect 

 and transmissibility of acquired characters, for the multicellular 

 he is rigidly and entirely his opponent, 



Inseparably bound up with the theory of the continuity of the 

 germ plasma is the assumption of the great difference which 

 obtains in respect of the transmissibility of characters which are 

 congenital, and characters which are acquired ; and so much im- 

 portance does Weismann lay upon a sharp and clear distinction 

 being made between these two kinds of characters, that I had 

 best quote the words of his own essay on this part of the sub- 

 ject : — " It is certainly necessary to have two terms which dis- 

 tinguish sharply between the two chief groups of characters — the 

 primary characters which first appear in the body itself, and the 

 secondary ones which owe their appearance to variations in the 

 germ, however such variations may have arisen. We have 

 hitherto been accustomed to call the former ' acquired characters,' 

 but we might also call them somatogenic, because they follow from 

 the reaction of the soina under external influence, while all other 



