4i8 HEREDITY AND DEVELOPMENT 



tion of the bi-parental heritage varies greatly in each individual 

 case ; that the parental heritages include ancestral contributions 

 which may be expressed in development or may lie latent ; that 

 normal development implies an appropriate environment, and 

 that, during the development, there are subtle interactions 

 between the growing organism and this environment, and 

 between the different constituents of the growing organism ; 

 that the development is in certain aspects like the building-up 

 of a mosaic out of many independently heritable and variable 

 parts, and that it is in other aspects the expression of an 

 integrated unity, with subtle correlations between the parts, 

 and with remarkable regulative processes working towards an 

 unconsciously predetermined end \ that in a general way the 

 individual development of organs progresses from stage to 

 stage in a manner which suggests a recapitulation of the steps 

 in racial evolution ; that many items in the inheritance, pre- 

 sumed to be present because of their re-expression in subsequent 

 generations, may lie latent and find no realisation in the in- 

 dividual development ; that minute peculiarities of an ancestor 

 may be handed on from generation to generation, although other 

 peculiarities of that ancestor find no expression ; that the 

 offspring of two parents differing in regard to some well-dehned 

 character may all resemble one parent as regards that character ; 

 that the inbred offspring of these hybrids may have offspring 

 divisible into two groups, one group resembling the one ancestor 

 and the other group resembling the other ancestor ; that in 

 other cases the expressed inheritance seems as if it were a mosaic 

 of ancestral contributions from parents, grandparents, great- 

 grandparents in a diminishing geometrical ratio according to 

 the remoteness of the ancestors : and we know much more 

 than all this ! 



A Glimpse of our Ignorance. — On the other hand, we have 

 still to confess our inability to solve the old problems : How 

 are the characteristics of the organism potentially contained 



