180 Inheritance of Acquired Characters 
any argument against the inheritance of acquired char- 
acters. The continuous electric current for example can 
be produced by a battery as well as by a dynamo; and 
the fact that one can always explain it as having been pro- 
duced by a battery does not prevent it from being actually 
produced by a dynamo in many cases. 
This being so, let us now examine as succinctly and 
objectively as we can each of the four arguments: 
1. No value can be attributed to the fact of the 
exercise of a function only a single time during life. 
In the first place, it is possible that it may formerly have 
been exercised repeatedly by the ancestors of individuals 
now living. In the second place this singleness does 
not exclude in any way its inheritance as a habit acquired 
by exercise. For the fact of having performed a given 
function even though only a single time, would certainly 
leave in the parent organism a potential disposition to 
perform it again and with greater facility in similar 
physiological and external circumstances; therefore 
the conception that this disposition and this greater 
facility would be represented in descendent organisms 
represents only an ordinary case of inheritance. 
2. As for the second argument one cannot but 
recognize that for certain formations the statement of 
Weismann that they can be due only to natural selection 
seems very probably true. 
But it must be remarked that to support his assertion 
Weismann attributes a merely passive function to many 
parts in which it is very questionable. 
Why for instance should we not regard the carapace 
of the turtle as a true and functional adaptation due to 
the stimulus of the environment to which the skin of 
the animal had reacted by a secretion constantly richer 
