THE THEORY OF DESCENT 281 



But enough of possibilities. Let us be content at 

 present to know at least a few real instances with regard 

 to the slowness of the process of what might be said to be 

 " re-adaptation ' in some plants. This process shows us a 

 way by which our problem may some day be solved ; it 

 allows us to introduce inheritance of acquired characters as 

 a legitimate hypothesis at least, which not only will explain 

 many of the diversities in systematics historically, but also 

 can be called, though not a causa vera, yet certainly more 

 than a mere fiction. 



OTHER PRINCIPLES WANTED 



We have only dealt with the probability of the 

 inheritance of morphological or physiological l adaptation. 

 If that could really be considered as one of the factors 

 concerned in the theory of descent, many, if not all of those 

 congenital diversities among organic species which are of 

 the type of a true structural correspondence to their future 

 functional life, might be regarded as explained, that is, as 

 reduced to one and the same principle. But nothing more 

 than an explanation of this kind of diversities is effected 

 by our principle, and very much more remains to be done, 

 for organic diversities not only consist in specifications and 



lished very important experiments on the inheritance of "acquired' 1 

 modifications with regard to the peculiarities of reproduction in Salamandra 

 atra and #. viaculosa. It seems rather improbable though not absolutely 

 impossible that the germ cells were directly affected by the external 

 modifying agent in this case. 



1 We have not spoken about the hypothetic inheritance of pure physio- 

 logical adaptations, for it is clear without further discussion that innate 

 specific immunity, for instance, being a specific " adaptedness " (sec p. 186) 

 might be due to the inheritance of the results of active immunity as an 

 adaptation, just as adaptive congenital structures 'tiiight be due to such 

 an inheritance. 



