214 The American Naturalist. [March, 
vary simultaneously“ (e. g., fore and hind limbs, or a series of 
vertebrz), we have still further to assume that these variations are 
selected with codrdinate variations in parts which are not in the 
remotest degree correlated, viz., the teeth.” We must still fur- 
ther assume that Selection acts at the same rate to produce simul- 
taneously exactly parallel lines of adaptive variations in related 
species over widely distributed areas, as in the American and 
European species leading to the horse series. If it is maintained 
that this parallelism has been sustained by interbreeding, then the 
arguments based upon Divergence and Isolation lose their force. 
If it be said that combinations of favorable variations occur in 
nature, not only in correlated but in uncorrelated parts, and Selec- 
tion acts upon these combinations, then those who support Weis- 
mann’s principle must further assume that there are definite lines 
of blastogenic variation. This argumentum in circulo would 
bring us back to the original question, What is the cause of defi- 
nite lines of variation ? 
Can Acquired Variations be Inherited ?—It must be admitted by 
every one that, as the germ-cells are usually differentiated and set 
apart from the somatic cells at an early age, it is very difficult to 
conceive how definite changes in certain peripheral somatic cells 
occurring in the higher adult Metazoa can produce such changes 
in the germ-cells as to be reproduced in the offspring, even if we 
allow a very long time for the process. If, however, such a process 
does take place, it rests with the embryologists to work out a 
theory for it, so we are not concerned with the process, but the 
evidence. All the evidence above considered belongs properly to 
Evolution; we must now consider the bearings of some of the 
classes of evidence from Inheritance. 
_. The evidence from mutilations is somewhat conflicting. It has 
been fully discussed recently by Weismann, Eimer, and others. 
It involves two elements which are not observed in the ordinary 
course of evolution: 1. Immediate transmission of the full charac- 
ters. 2. Transmission of characters impressed upon the organism, 
* The fact that they do so may be used as an indirect argument for the Lamarck- 
® Or adaptive characters for protection, mimicry, sexual ornamentation, etc. 
ae ee eee eee 
