Weismann’s Arguments Against Inheritance 1 77 
furnishes us itself a proof of this. For from the first 
impact against the glass partition the inclination con- 
trary to its instinct must have commenced to arise; 
nevertheless it effected the replacement of the latter 
only after a large number of unavailing attempts. 
From all that we have said thus far it follows that 
it is much to be desired that new and absolutely incon- 
testable experiments should once for all finally place the 
inheritance of acquired characters beyond a doubt. But 
it also follows, as we have said, that if no one of the 
proofs which we possess already demonstrates this in- 
heritance in an absolutely certain way, nevertheless all 
together they supply a great weight of evidence for it. 
As we shall see later this is true also of indirect proofs; 
one cannot say of any one of them that it decides the 
question in one way or the other, but all together 
they constitute a strong presumption in favor of the 
Lamarckian theory. 
It will be convenient to examine next the chief argu- 
ments which Weismann has adduced against this theory. 
They can be reduced in substance to the following: 
1. “In many animals,” he writes, “for instance in 
many insects, instincts appear which are exercised only 
once during life. It is sufficient to cite the laying of 
eggs by ephemerids and many butterflies, the conjugation 
of bees, the search for proper hiding places in which 
caterpillars may change into chrysalids,—one species 
suspends itself, another lying on the ground builds de- 
fences, a third goes deep into the earth, a fourth spins 
itself a case in a rolled up leaf, and so on, and so on. 
Further there belong here the several species of cocoons 
which some butterflies, especially the bombycids, spin 
in a fashion so astonishingly complicated and so well 
