668 The American Naturalist. | [August, 
more an embryological matter than a philosophical one. We 
are particularly concerned in its results, which are the distin- 
guishing marks of Neo-Darwinism—that variation is of sexual 
or internal origin, and that acquired characters are not her- 
editary. 
In opposition to this body of belief, which has been upheld, 
` particularly in England, with much aggressiveness, is Neo- 
Lamarckism, which is a compound of both Lamarckism and 
Darwinism, and which has an especially strong following in 
North America. The particular canons of this philosophy are 
the belief that external causes, or the environment, are directly 
responsible for much variation and that acquired characters 
are often hereditary. Other features of it, held in varying 
degrees by different persons, are the belief in the transforming 
effects of use and disuse, and in natural selection. 
The one great schism between the Neo-Darwinians and the 
Neo-Lamarckians is the controversy over the hereditability of 
acquired characters, and just at present this question has come 
so strongly to the fore that other differences in the two hypothe- 
ses have been obseured. Itis worthy of remark that Darwinism 
or Neo-Lamarckism sees first the facts or phenomena and then 
tries to explain them; while Neo-Darwinism or Weismannism 
assumes first a hypothesis and then tries to prove it. Ithink 
that any one will be struck with this difference of attitude, if 
he read Darwin's ehapter upon pangenesis, and then read 
Weismann's essay upon heredity. The Neo-Darwinians areloud 
in demand of facts or proof that aequired characters are her- 
editary, and they attempt to throw the burden of proof upon 
their opponents; while, at the same time, they give no proofs 
of their own position, and confound their adversaries with 
verbal subtleties. The burden of proof, however, lies clearly 
upon the Neo-Darwinians, inasmuch as they have assumed to 
deny phenomena which were theretofore considered to be estab- 
lished. 
A voluminous issue of polemics has occurred during the last 
five or six years between the Neo-Darwinians and the Neo- 
Lamarckians; but whatever may have been its effects upon 
the older philosophy, it is clear, to my mind, that some of the 
