The Inheritance of Acquired Characters 51 
assumption, not only in the restricted sense as defined above, 
but also in the sense that external conditions may directly affect 
the whole organism, i.e. germ-cells as well as the body-cells. 
He made no such sharp distinction, however, between these two 
sides of the question as we find it convenient to make nowa- 
days. 
Let us examine critically the experimental evidence on which 
the theory of the inheritance of acquired characters, in the 
restricted sense, rests, for, could it be shown that changes 
acquired through use are transmitted to the next generation, we 
might seem to be able to explain how many of the complicated 
adaptations and coérdinations of animals have arisen. 
Amongst modern writers the first to seriously question the 
truth of the generally admitted doctrine that acquired charac- 
ters are inherited was August Weismann. In his essay “On 
Heredity,”’ published in 1883, and in two subsequent papers 
“On the Supposed Botanical Proofs of the Transmission of 
Acquired Characters” (1888), and ‘The Supposed Transmis- 
sion of Mutilations’” (1888), Weismann challenged the ac- 
cepted point of view. His conclusions have become common 
knowledge, so that it will not be necessary to go over the ground 
again. While many zodlogists and botanists were convinced 
by Weismann’s argument, which seemed to show that the evi- 
dence fails to support the view that acquired characters are 
inherited, a few zodlogists have always insisted nevertheless 
that such characters are inherited, and a few investigators have 
brought’ forward experimental evidence which they believe 
shows convincingly that changes brought about in the body 
may be transmitted to the germ-cells. It is this experimental 
evidence that I propose éspecially to consider. 
Darwin believed that acquired characters are inherited, and 
in the “Origin of Species,” in the ‘Animals and Plants under 
Domestication,” and in the ‘Descent of Man” he accounts for 
many adaptations in this way. Herbert Spencer, especially, 
although not always with discrimination, used this hypothesis to 
account for many structures and habits of animals and plants. 
