Copy I do not think I have any remark to make on the above letter except to state that until I saw it I had not read or heard of the Rev. J.T. Gulick's memoir. Having done so since, I feel rather overwhelmed with the mountain of terminology and the hillock of Statistical fact. I see therein no numerical proof that fertility is inherited or that it is correlated with other characters. But it is such proof with which I personally am alone concerned. All sorts of factors of evolution are day by day propounded by biologists; I may be right or I may be wrong, but I held that their discussion is worthless until they are brought to the test of facts and analysed by the mathematical theory of statistics. The opening words of my memoir on Reproductive selection fully express my standpoint "I understand by a factor of evolution any