176 CONTINUITY OF THE GERM-PLASM AS THE [IV. 



evidence can be brought forward. In the following pages I 

 shall attempt to develope further the theory of which I have 

 just given a short account, to defend it against any objections 

 which have been brought forward, and to draw from it new 

 conclusions which may perhaps enable us more thoroughly to 

 appreciate facts which are known, but imperfectly understood. 

 It seems to me that this theory of the continuity of the germ- 

 plasm deserves at least to be examined in all its details, for it 

 is the simplest theory upon the subject, and the one which is 

 most obviously suggested by the facts of the case, and we shall 

 not be justified in forsaking it for a more complex theory until 

 proof that it can be no longer maintained is forthcoming. It 

 does not presuppose anything except facts which can be ob- 

 served at any moment, although they may not be understood, — 

 such as assimilation, or the development of like organisms from 

 like germs ; while every other theory of heredity is founded on 

 hypotheses which cannot be proved. It is nevertheless possible 

 that continuity of the germ-plasm does not exist in the manner 

 in which I imagine that it takes place, for no one can at present 

 decide whether all the ascertained facts agree with and can be 

 explained by it. Moreover the ceaseless activity of research 

 brings to light new facts every day, and I am far from main- 

 taining that my theory may not be disproved by some of these. 

 But even if it should have to be abandoned at a later period, it 

 seems to me that, at the present time, it is a necessary stage in 

 the advancement of our knowledge, and one which must be 

 brought forward and passed through, whether it prove right 

 or wrong, in the future. In this spirit I offer the following 

 considerations, and it is in this spirit that I should wish them 

 to be received. 



I. The Germ-plasm. 



I must first define precisely the exact meaning of the term 

 germ-plasm. 



In my previous writings in which the subject has been 

 alluded to, I have simply spoken of germ-plasm without indi- 

 cating more precisely the part of the cell in which we may 

 expect to find this substance — the bearer of the characteristic 

 nature of the species and of the individual. In the first place 

 such a course was sufficient for my immediate purpose, and 



