THEORIES OF HEREDITY 75 



said is, that it is so. The child can predominantly resemble 

 one parent only. The cases of hybridization, as quoted 

 already, show that, in the crossing of different species, the 

 characteristics of one parent may be suppressed nearly to 

 complete exclusion, thereby proving that the determining 

 power of the Ids of one parent may fall to zero in the pres- 

 ence of a stronger set of determinants of the other parent. 

 We may in the same way explain the predominant inherit- 

 ance of individual traits by assuming that the Ids of one 

 parent, though present, do not come to expression in the 

 developing organism. Father as well as child may be 

 predominantly shaped by the influence of the same set of 

 Ids that is, those derived in each case from the father 

 while those of the mother remain unexpressed. In 

 Fig. 41, if the black Ids are in each case predominant, the 

 father (second generation) and the child (third generation) 

 would resemble each other, showing the black type ex- 

 clusively. 



Another possibility lies in the fact that the number of 

 homodynamous determinants may be greater in the Ids 

 of the father than in those of the mother, so that, by acting 

 in unison, they would overcome the smaller number of those 

 of the mother. 



As the number and power of the homodynamous deter- 

 minants may vary for each particular stage of the child's 

 development, we find in the same circumstance also the 

 explanation for particulate inheritance of individual traits. 



B QUANTITATIVE CONTRIBUTION OF ANCESTORS. 



It is generally reckoned that the parents contribute to 

 the heritage of the child J each ; each grandparent, J ; 

 each great-grandparent, J, etc. But though each parent 

 furnishes half the hereditary substance of the offspring, 

 the proportions for grandparents, etc., are by no means 

 necessarily expressed by J, J, etc. For if we assume the 

 species to have 16 Idants (see Fig. 41), grandfather as well 



