REPRODUCTION 95 



deformities and defects, such as short fingers, 

 aborted fingers, split fingers, split foot, catar- 

 act, certain hair deficiencies, stationary night- 

 blindness, certain sex-limited diseases like 

 haemophilia, and color-blindness ; and certain 

 kinds of deaf-mutism, insanity, and imbecil- 

 ity. Thus even at this early stage in the 

 study of human heredity, there is good reason 

 to believe that many of our traits Mendelize. 

 But the question that confronts the modern 

 student of genetics is the extent to which 

 Mendelism may be said to apply. Are all 

 characteristics in man and other animals in- 

 herited in accordance with these principles, or 

 are only a part of them so handed on? Man 

 himself seems to offer some very interesting 

 examples that are very difficult to bring un- 

 der the Mendelian rules. Thus, when the white 

 man is crossed with the negro neither one nor 

 the other is produced, but an intergrade, the 

 mulatto. Inheritance of this kind is called 

 blended and is represented by many examples. 

 Whether it is a form of Mendelism in which 

 dominance is absent is not clear. Possibly it 

 is a totally different method of inheritance 

 from that exemplified in the Mendelian cases. 

 Certainly so long as instances of this and other 



