130 FOOT-NOTES TO EVOLUTION. 
Lamarck’s much-discussed “ fourth law ” of develop- 
ment reads as follows: “All that has been acquired, 
begun, or changed in the structure of the 
individuals in their lifetime is preserved 
in reproduction and transmitted to the 
new individuals which spring from those 
who have inherited the change.” 
“Change of function produces change of structure,” 
so Herbert Spencer tells us; “it is a tenable hypothesis 
that changes of structure thus produced are inheritable,” 
But though this may be a tenable hypothesis, the 
opposite hypothesis has not been clearly shown to be 
intenable. It seems to be true that any great physical 
weakness on the part of Richard Roe’s parents would 
tend to lower his constitutional vigour, whatever the 
origin of such weakness might be. If so, such weakness 
might appear as a large deficiency in his power of using 
his equipment. It may be, too, that any extreme degree 
of training, as in music or mathematics, might determine 
in the offspring the line of least resistance for the move- 
ment of his faculties. Perhaps Richard Roe would find 
Inheritance of 
acquired charac- 
ters. 
force on the generation that develops them. Acquired characters 
are never inherited. Other investigators, equally wise, Herbert 
Spencer and Lester F. Ward, for example, do not admit that any 
gain or loss to the individual is without its effect on succeeding 
generations, and thus on the species. X and Y are inherited just 
as B or B' may be. 
Let us assume that they are inherited in some degree, and let us 
X+X'-Y-Y’, 
Q 
The divisor Q reducing all acquired characters of the parent is an 
unknown quantity of large and perhaps variable value. If large, 
the value of the fraction will be correspondingly small. In Weis- 
represent this inheritance of acquired characters as 
mann’s view, Q should equal infinity, in which case 5 or 5 would 
be nothing at all. This would be the symbol of non-inheritance. 
