74 THE MENDEL JOURNAL 



the standpoint of the type of offspring which we may 

 expect, we have two real combinations within this 

 one visible one, i.e., D D x R R and D R x R R. 

 In the first case all the offspring are expected to have 

 duplex eyes, and in the latter one-half is expected 

 to show the duplex eyes and the other half simplex. 

 What are the actual results ? There were seventeen 

 pairs of parents, of the nature of Duplex x Simplex, 

 with a total of sixty-six offspring all showing the 

 duplex type of eye. And there were fifty-two other 

 pairs of parents of the same visible nature who had 

 a total offspring of two hundred and fifty-eight, one 

 hundred and thirty-seven of whom had the simplex 

 eye and one hundred and twenty- one the duplex eye. 

 The expectation is one hundred and twenty-nine of 

 both types. There is thus a very near approximation 

 of result to prediction. 



Mr. Hurst's work shows two things quite clearly. 

 It demonstrates the absolute segregation of these 

 two types of eyes in human inheritance, and compels 

 us to accept the conception of gametic purity as 

 the only vaUd explanation of it. It is quite evident 

 that the alternative hypothesis of blended inheritance 

 does not explain a single feature of the phenomena. 

 For if it did, why do blue-eyed (simplex type) offspring 

 come from two brown-eyed (duplex) parents ? Or, 

 why do they come from parents one of whom has 

 brown eyes and the other blue ones ? Why do some 

 brown-eyed pairs of parents give nothing but dark- 

 eyed offspring, and other pairs give a mixed offspring 

 of dark-eyed and blue-eyed individuals ? The con- 



