68 BASIS OF THE PROBLEM 



are similar, the adult forms will differ. The larger members of 

 each of these pairs may thus resemble one another very closely 

 in outward characters ; but this close resemblance will not be due 

 to similar germinal constitutions. It follows that by mere outward 

 inspection no conclusion can be reached as to the germinal con- 

 stitution. There are, therefore, two classes of influences at work, 

 and alterations in either class of influence will bring about altera- 

 tions in the resulting organism ; similar characters may be the 

 product of one kind of predisposition and one kind of stimulus, 

 or of a different predisposition and a different stimulus. It also 

 follows that we cannot speak of certain characters as inherited 

 and of others as acquired. Let us suppose that some departure 

 from the normal structure occurs. It may be due to a change 

 in the environment, that is to say, to a new stimulus acting upon 

 an unchanged germinal constitution, or it may be due to a change 

 in the germinal constitution when no change in the environment 

 takes place. It should not be said that in the former case the 

 new departure is acquired and in the latter case that it is inherited. 

 What has happened is that in the former case a new stimulus 

 acting upon the old factors has brought forth a new character, 

 and in the latter case that the old stimulus has brought forth 

 a new character because it has acted upon a different factor. 



Though the popular distinction between characters which are 

 acquired and characters which are inherited is misleading, there 

 are, nevertheless, two kinds of variation. A new departure may 

 be due to a change in the germinal constitution. In tliis case 

 the new character will reappear in future generations, provided 

 that the changed germinal constitution remains and provided 

 that the complex of stimuli which composed the environment 

 does not change. Such a variation may be called a ' mutation '. 

 A new departure may also be due to a new stimulus acting upon 

 an unchanged germinal constitution. In this case the new 

 character will only reappear in future generations provided that 

 the new stimulus remains. Such a variation may be called 

 a ' modification '. Mutations, therefore, are transmitted in the 

 germinal constitution, while modifications are not so transmitted. 



4. Already we have reached the answer to the first problem. 

 Permanent change in organic form is due to germinal change. 

 But before we go on and ask how germinal changes, that have 

 arisen, become established, we must consider further the difficult 



