98 The Third and Fourth Generation 



numbers of each, since the chances are equal 

 that the egg will be fertilized by either sort 

 of sperm. The expected Mendelian phenom- 

 enon does not appear, for we should anticipate 

 that in crossing a red-eyed with a white-eyed, 

 the Fi generation would be all either red or 

 white, depending on which character is domi- 

 nant. But if we make the supposition sug- 

 gested, viz., that the factor for red eye is 

 carried by the sex chromosome, the facts found 

 are adequately explained by the hypothesis, and 

 this does no violence to Mendel's law. It is 

 merely an extension of it. 



There is one form of color blindness in human 

 beings that is customarily confined to men. 

 Still, the daughter of such a color-blind father, 

 though herself normal, may transmit the 

 difficulty to some of her sons. If we suppose 

 that the factor for the perception of color is 

 carried in a sex chromosome, color-blind men 

 would be represented thus, [o]; and the normal 

 female so, @. The eggs from the female will 

 be all of one type, (•); the sperm from the 

 male of two sorts, one with the sex chromo- 



