Similarity of Adaptations in Different Species 207 
cussed, it may merely be remarked here that the existence 
of these like properties, acquired in the most different 
species, is easier to explain by the Lamarckian theory than 
by natural selection. For just as substances exposed, for 
example, to identical calorific influences finally all take 
on the same degree of temperature, and yet all remain 
quite different from one another in other characters, 
so when quite different species are exposed, on account 
of the environment, or nourishment, or peculiar condi- 
tions of light, or of any other cause whatever, to func- 
tional stimuli which incite them, for example, to secrete 
tannic acids or alkaloids, and so on, these secretions, 
acquired by means of functional adaptation and trans- 
mitted later by heredity, must come to be present in 
several species, even though all other characters can 
remain different. 
Here it seems to us, there remains for Weismann 
nothing else than to affirm that these like characters 
may have been fixed by natural selection in the most 
different species because, from the likeness of the func- 
tional stimuli to which, according to the hypothesis, these 
species were exposed, the same characters must have 
been the most useful for every one without exception. 
But this must first be proved. And so much the more 
since in this case it is more difficult than in other cases 
to see the absolute necessity that all characters or pecu- 
liarities whatever, which are due to the reaction of the 
organism to the most different external influences and 
often to insignificant ones, must always be useful to 
the individual, and that therefore they must also possess 
this utility even when they are produced rather by means 
of inborn fortuitous variations. 
If the soundness of this conception, required by the 
