726 THE AMERICAN NATURALIST [Vol. XLIV 



cent. ; with 10 or more children to 23 per cent. On the 

 average, with the larger families the proportion of al- 

 binos tends to approach expectation. 



A second source of error is not to be neglected. When 

 the attention of the parent or acquaintance is focused 

 by the questioner upon albinos the albinic children are 

 all recalled, while some normal children (such as were 

 still-born or died in infancy) are more apt to be for- 

 gotten. I have repeatedly had the experience of bringing 

 to mind by further questioning children that had not 

 been at first mentioned, and they were always normal 

 children. The records of families with only one child 

 and that an albino are frequently due to the fact that the 

 peculiar child is the only one recalled. Considering the 

 high frequency of infant mortality the omission of nor- 

 mal children forms an important factor tending to raise 

 the proportion of albinos. 



A third possible source of error lies in imperfection of 

 dominance, i. e., the occasional failure of the pigment to 

 show itself in the young chlidren who have it simplex. 

 Of this imperfection there are all degrees. Thus 

 the albinos in the Lie (No. 14) and Moo (No. 17) families 

 have a dark retina with white hair, washed-out blue iris 

 and nystagmus. In other cases, such as the Kid familv 

 (No. 20) and P-W,a (XII, 24, 25), the hair is yellowish, 

 while the retina is pink, or the pinkish retinal glow and 

 nystagmus may be slight. Another fact that favors the 

 view of frequent failure of the simplex determiner to 

 activate fully is the progressive increase in pigmentation 

 shown by some albinos. This is a common phenomenon. 

 Seligsohn in Eulenburg's "Keal Encyclopadie, 9 ' 1880, 

 p. 162, states: "Bei einem vongesunden Eltern mit alien 

 Morknialen einer Albino geborenen Kinde schwand die 

 rothe Farbe der Iris von Jahr zu Jahr." This increase 

 m development of a simplex character has been observed 

 by Lang in snails, by one of us in poultry and bv others. 



In concluding this discussion of the causes of the aber- 

 ration m the proportion of albinos I wish to urge that 



