INHERITANCE OF ACQUIRED CHARACTERS 77 



and we know that continuous variations are in- 

 herited. 



On the other hand, several lines of inquiry have 

 separately led to the conclusion that a great number 

 of the visible characteristics of organisms are of a 

 definite kind, and are inherited definitely, their appear- 

 ance being determined by the presence of definite 

 structures or substances in the germ-cells. The evi- 

 dence, as we shall see later on, points to the conclusion 

 that such characters have arisen suddenly at a single 

 step, and we must conclude that in such a case a definite 

 change in the germinal structure has been followed by 

 a definite alteration in the character of the organism 

 arising from the germ ; since no one can suppose that a 

 large and definite structural alteration can be first 

 acquired by the adult organism and then inherited by 

 its offspring such a process is unthinkable. 



Thus we see that the inheritance of acquired char- 

 acters, if such inheritance really takes place at all, 

 must be confined to the transmission of changes of an 

 indefinite and quantitative kind to the case, in fact, of 

 continuous variations or individual differences. More- 

 over, there is nothing to show that all continuous 

 variations are not of the nature of acquired characters.* 



* We know, at any rate, that continuous variations are not 

 invariably due to the cause which Weismann supposed namely, 

 to the mingling together of characters derived from the two 

 parents a supposition which is of fundamental importance 

 to his theory because, as Karl Pearson has pointed out in 

 this connection, parthenogenetically reproduced organisms, 

 in which no such mingling has taken place, may be just as 

 variable as those which owe their origin to the process of 

 sexual generation. 



