r explanation. The
other school is equally insistent that there are abundant instances of
the inheritance of acquired characters, claiming that these proofs are
so strong as to demand their acceptance. Hence this class of biologists
insist that the explanation of heredity given as a simple handing down
from generation to generation of a germ plasm is not complete, and that
while it is doubtless the foundation of heredity, it must be modified in
some way so as to admit of the inheritance of acquired characters. There
is no question that has excited such a wide interest in the biological
world during the last fifteen years as this one of the inheritance of
acquired characters. Until about 1884 the question was not seriously
raised. Heredity was known to be a fact, and it was believed that while
congenital characters are more commonly inherited, acquired characters
may also frequently be handed down from generation to generation. The
facts which we have noted of the continuity of germ plasm have during
the last fifteen years led many biologists to deny the possibility of
the latter. The debate which arose has continued vigorously, and can not
be regarded as settled at the present time. One result of this debate is
clear. It has been shown beyond question that while the inheritance of
congenital characters is the rule, the inheritance of acquired
characters is at all events unusual. At the present time many
naturalists would be inclined to think that the balance of evidence
indicates that under certain conditions certain kinds of acquired
characters may be inherited, although this is still disputed by others.
Into this discussion we cannot enter here. The reason for referring to
it at all is, however, evident. We are searching for nature's method of
building machines. It is perfectly clear that variations among animals
and plants are the foundations of the successive steps in advance made
in this machine building, but of course only such variations as can be
transmitted to posterity can serve any purpose in this development. If
therefore it should prove that acquired characters can not be inherited,
then we should no longer be able to look upon the direct influence of
the surroundings as a factor in the machine building. We should then
have nothing left except the congenital variations produced by sexual
union, or the direct variation of the germ plasm as a factor for
advance. If, however, it shall prove that acquired charact