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THE AMERICAN NATURALIST [Vol. L 



If you like to form a definite idea you might assume that 

 the potency means a certain concentration of enzyme 

 which acts according to well-known laws. 4 In order to 

 make the situation clear we assume that we are able to 

 measure their potency. And we find that the female 

 factorial set [ff| is 80 units strong and every male factor 

 M = 60 units. Then in the female formula jFF) Mm the 

 female set overpowers the one M present by 20 units, 

 whereas in the male formula jFF| MM the two Ms with 

 the value of 120 are 40 units stronger than [ff] = 80. 

 Now we face two possibilities. Either the slightest pre- 

 ponderance of one set over the other, say by only one 

 unit, is sufficient to determine the male or female sex, 

 or there is a definite minimum of preponderance neces- 

 sary—we call it the epistatic minimum— beyond which 

 one or the other sex appears. Let us now suppose this 

 minimum to be 20 units. Then of course 40 units are 

 left between the two extremes male-female preponder- 

 ance. If we call the difference value between the male 

 and female factorial set e, then we have a female, when 

 [FF] — M = > 20 and a male, when MM — [ff| > 20, or 

 in other words the limiting values for e for the two sexes 

 are + 20 and — 20. We can now express this conception 

 graphically in the following diagram, where the values 



of e are arranged on a straight line. Individuals to the 

 right of -f 20 are females, to the left of — 20 are males. 

 But what of the intermediate points? These are the 

 intersexual animals ; if they are heterozygous for M they 

 are intersexual females and if they are homozygous for M 

 they are intersexual males. How does this diagram now 



