FOUNDATION OF A THEORY OF HEREDITY. 173 



must be a direct connexion between the germ-cells of succeeding 

 generations, and they tried to establish such a continuity by sup- 

 posing that the germ-cells of the offspring are separated from the 

 parent germ-cell before the beginning of embryonic development, 

 or at least before any histological differentiation has taken place. 

 In this form their suggestion cannot be maintained, for it is in 

 conflict with numerous facts. A continuity of the germ-cells does 

 not now take place, except in very rare instances ; but this fact 

 does not prevent us from adopting a theory of the continuity of 

 the germ-plasm, in favour of which much weighty 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 im- 

 perfectly understood. It seems to me that this theory of the con- 

 tinuity 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 until proof that it can be no longer maintained is forthcoming.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 observed 

 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 



exceedingly feeble, because ' the effects of the use and disuse of limbs, and those of 

 habit, are transmitted to posterity in only a very slight degree.' He also argues that 

 many instances of the supposed transmission of personal characters are really due 

 to latent equivalents. 'The personal manifestation is, on the average, though it 

 need not be so in every case, a. certain proof of the existence of latent elements.' 

 Having argued that the strength of the latter in heredity is further supported by 

 the facts of reversion, Galton considers it is safe to conclude 'that the contribution 

 from the patent elements is very much less than from the latent ones.' In the 

 later development of his theory, Galton adheres to the conception of ' gemmules ' 

 and accepts Darwin's views, although ' with considerable modification.' Together 

 with pangenesis itself, Galton's theory must be looked upon as preformational, and 

 BO far it is in opposition to Weismann's theory which is epigenetic. See Appendix 

 IV. to the next Essay (V.), pp. 316-319. E. B. P.] 



