THE PHENOMENA OF REVERSION 3O9 



which are present in the largest numbers always have the best 

 prospect of controlling the cell entirely, or at any rate chiefly ; 

 their effect must be cumulative, and a small minority of homo- 

 dynamous determinants will not be able to take effect against a 

 large majority of some other variant. The control of the cell 

 therefore results from this struggle of the determinants, which 

 must naturally not be conceived to take place in such a manner 

 that the group of paternal ids struggles with the maternal group, 

 but so that all the active determinants which are contained in 

 the idioplasm migrate into the cell body and there strive to 

 obtain the control. If the parents of the organism in question 

 are closely related, the same homodynamous determinants may 

 very possibly be contained in the idants of both parents, and 

 the forces of these will then combine just as would be the case 

 if they had been contained in one idant of the father or mother. 

 It will, however, happen more frequently that homodynamous 

 determinants are present in the ids of each parent respectively, 

 and a majority of homodynamous maternal determinants will 

 then compete with a majority of paternal ones; they will then 

 either control the cell together, or the prepotency of one of 

 the parents will be so great as to suppress the influence of the 

 other entirely. 



In order to test to what extent these ideas of the co-operation 

 of parental idioplasms may be applied to the phenomena of 

 reversion in Man, we must again consider the simplest of these 

 phenomena, viz., that oi reversion to a grandparent . 



It is well known that a child not infrequently resembles its 

 father or mother in a high degree, and it is also assumed that a 

 father may beget a child which does not resemble him, but it 

 and its father's mother are as 'like as two peas.' This pre- 

 supposes that the father himself bore no resemblance to his 

 mother, for otherwise it would not be an instance of reversion 

 of the child to the grandmother. 



This case may be explained theoretically by assuming that 

 the ' reducing division ' of the respective germ-cells of the two 

 generations accurately separated the paternal from the maternal 

 idants, and that, as was shown above, the group of idants of 

 one of the parents may possibly have had no influence on the 

 formation of the child, the other group being the dominant one. 

 The fertilised egg-cell from which the father was developed 

 must therefore have contained the two groups of idants A and 



