Inheritance of Physical and Mental Traits 271 



there a determiner for iris pigmentation; consequently in 

 respect to brown iris pigmentation such a person may be 

 said to be nulliplex. If now such a person marry an indi- 

 vidual duplex in eye color, in whom all of the germ cells 

 contain the determiner, each child will receive the deter- 

 miner for iris pigmentation from one side of the house only. 

 This determiner will, of course, induce pigmentation, but 

 the pigmentation is simplex, being induced by one deter- 

 miner only. Consequently, the pigmentation is apt to be 

 weak. When a person whose pigment determiners have 

 come from one side of the house forms germ cells, half 

 will have and half will lack the determiner. If such a 

 person marry a consort all of whose germ cells contain the 

 determiner for iris pigmentation, all of the children will, of 

 course, receive the iris pigmentation, but in half it will be 

 duplex and in the other half it will be simplex. If the two 

 parents both be simplex, so that, in each, half of the germ 

 cells possess and half lack the determiner in the union of 

 germ cells, there are four events that are equally apt to 

 occur: (i) an egg with the determiner unites with a sperm 

 with the determiner; (2) an egg with the determiner unites 

 with a sperm without the determiner; (3) an egg without 

 the determiner unites a sperm with the determiner; (4) an 

 egg without the determiner unites with a sperm without the 

 determiner. Thus the character is duplex in one case, 

 simplex in two cases, and nulliplex in one case; that is, one 

 in four will have no brown pigment, or will be blue eyed. 

 If one parent be simplex, so that the germ cells are equally 

 with and without the determiner, while the other be nulli- 

 plex, then half of the children will be simplex and half 

 nulliplex in eye pigment. Finally, if both parents be nulli- 

 plex in eye pigmentation (that is, blue eyed), then none of 



