OBITUARY 291 
‘resulting from the ae of the former. Nor 
is it essential that one should take up any 
particular position in regard to the mode of 
yariation, whether, for example, it takes place per 
saltum or gradually; whether it is definite in 
character or indefinite. Still less are those who 
‘accept the theory bound to any particular views as 
to the causes of heredity or of variation. 
_ That Darwin held strong opinions on some or all 
of these points may be quite true; but, so far as 
the theory is concerned, they must be regarded as 
obiter dicta. With respect to the causes of vari- 
ation, Darwin’s opinions are, from first to last, 
put forward altogether tentatively. In the first 
edition of the “ Origin,” he attributes the strongest 
influence to changes in the conditions of life of 
parental-organisms, which he appears to think act 
on the germ through the intermediation of the 
Sexual organs. He points out, over and over again, 
that habit, use, disuse, and the direct influence of 
conditions have some effect, but he does not think 
it great, and he draws attention to the difficulty 
: of distinguishing between effects of these agencies 
‘and those of selection. There is, boson one 
class of variations which he withdraws from the 
direct influence of selection, namely, the variations 
‘in the fertility of the sexual union of more or less 
closely allied forms. He regards less fertility, or 
more or less complete sterility, as “incidental to 
other acquired differences.” (Jbid., p. 245.) 
U 2 
