The Laws of Heredity. 1 8 1 



cites some instances of insanity which made its appearance at the 

 same age in several generations. One of these cases is that of a 

 grandfather, father, and son, who all committed suicide at about 

 the age of fifty ; another is that of a family all of whose members 

 became insane at the age of forty. 



Such facts as these and they are numerous are a strong argu- 

 ment in favour of the hypothesis of latent characteristics, and this 

 in turn does much to throw light upon many singular features of 

 heredity, as we can show by passing in review all the cases we have 

 cited. 



When the child takes equally after father and mother, the case 

 needs no explanation, it being the realization of the ideal law, as 

 far as that is possible. 



When the child resembles one of its parents to the exclusion of 

 the other, this exclusion does not really take place. That parent 

 whose influence appears destroyed may reappear in the next 

 generation, or later. 



It will be observed that the question already debated, ' whether 

 heredity is more frequent in one sex or between the two sexes/ 

 loses much of its importance when we regard heredity as a cycle. 

 When we see the father reappear in the daughter, and finally in 

 the grandson, the mother in the son, and finally in the grand- 

 daughter, we have no difficulty in believing that each sex reasserts 

 its rights, though it does not receive them at first 



Finally, the hypothesis of latent characteristics gives a plausible 

 and simple explanation of all the phenomena of reversion, whether 

 in direct or collateral line. 



Still it is evident that these formulas cannot pretend to give a 

 complete explanation of a fact so abstruse and so complex as 

 hereditary transmission. Our only purpose is to show that the 

 term is taken in too narrow a sense when it is restricted to two 

 generations, and that the facts seem less strange so soon as we 

 grasp them as a whole. We desired also to exhibit the wonderful 

 tenacity of heredity. Its law is absolute transmission; and, in spite 

 of all the obstacles which tend to weaken or destroy it, it struggles 

 on without truce or pause, losing much of its strength as it advances, 

 dissipating itself, so to speak, so as to appear no longer to exist. 

 And yet, when we see the same characters reappear, sometimes 



