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. 
