292 DAVENPORT— NEW VIEWS ABOUT REVERSION. [April 23. 



two eggs and these differences determine the different end results. 

 They may be called detenniners. Ordinarily, when parents are 

 similar, each unit character of the offspring develops from two 

 similar determiners — one paternal and one maternal. Thus in its 

 origin any unit character is duplex. When, however, the determiner 

 is found in only one of the parents the character is simplex. Now 

 such a character frequently develops imperfectly because of the 

 partial stimulus to development. 



If in an individual any character is simplex then the germ cells 

 of that individual are typically of two kinds ; half have the de- 

 terminer for the character and half lack such determiner. Now if 

 two such individuals be parents the chances of the uniting of 

 (o) two germ cells with the determiner, {b) two germ cells without 

 the determiner, and (c) one with and one without are as 1:1:2, or 

 25 per cent, of the offspring will have the character duplex ; 50 per 

 cent, will have it simplex, while 25 per cent, will lack the character 

 — and will thus resemble one of the grandparents ! 



To illustrate. If the two grandfathers have blue eyes and both 

 grandmothers brown eyes then the parents may both have simplex 

 brown eyes ; they will both form germ cells of which 50 per cent, 

 have and 50 per cent, lack the determiner to form brown iris 

 pigment. From such brown-eyed parents one child in four will have 

 blue eyes like the grandfathers. This is atavism. Cases of atavism 

 can, in general, be explained on the same ground as atavism to blue- 

 eyed grandparents. Complications are indeed induced by sex- 

 limited heredity, illustrated by the horns of sheep which appear, 

 when simplex, only in males of certain strains. A further complica- 

 tion is seen in cases of apparent or partial blending as in human 

 skin color. But in the great majority of cases atavism is a simple 

 reappearance in one fourth of the offspring of the absence of a 

 character due to the simplex nature of the character in both parents. 



Reversion in the strict sense has a more complicated explana- 

 tion. It depends in general on the circumstance that many appar- 

 ently simple organs or color patterns or colors are really complex 

 and require the cooperation of two or more elementary character- 

 istics called factors. For generations a particular character may 



