i 6 o 
A. D. Darbishire. 
as doing any more than submitting them to your consideration. 
But before I do so I should like to answer an objection which some 
among you may have been inclined to bring against my chronological 
delimitation of the three periods into which I have divided the 
history of the study of inheritance. You may object that the third 
period begins with the publication of Weismann’s Continuity of the 
Germ-Plasm in 1885, or Butler’s Life and Habit in 1877 or Mendel’s 
Versuche Tiber PJianzen-hybriden in 1865. This is not my meaning. 
By saying that during the 19th century investigation and speculation 
proceeded along wrong lines I do not mean that workers and 
thinkers who were on the right track did not exist during that period; 
but that the mass of biological opinion was on the wrong track. 
In fact my meaning cannot be better illustrated than by reference 
to the fact that the work of the three men who did most to bring 
about the return to the right track (Mendel, Butler, and Weismann—- 
I give their names in the order of the appearance of their most 
important works) although done roughly between 1860 and 1890, 
has not been understood and appreciated until recent years. I 
shall show, later on, that the work of Weismann is not, as it may at 
first sight appear to be, an exception to this statement. 
The Second Period. 
The great difference in the state of opinion between the age in 
which Erasmus and that in which Charles Darwin lived, was that 
the latter had succeeded, where his grandfather and Lamarck had 
failed, in convincing the intelligent public that the diversity of 
organic forms which people the earth had been brought about by a 
process of descent with modification. This in itself would not 
have made much difference. It is the theory advanced to account 
for this process which has had such a profound effect on the theory 
of inheritance. 
A theory of evolution having been established, two ways of 
accounting for the manner in which new characters arise and 
persist, were possible. The new character could arise either in 
the mature organism or in the germ which gave rise to it. Darwin 
chose the former alternative ; which made it necessary for him to 
put forward a theory to account for the manner in which the newly 
arisen character could be so impressed on the germ that it would 
be reproduced in the next generation. The theory which Darwin 
suggested was that of Pangenesis, which can be found in “ Animals 
