Other Kinds of Hybridizing 167 
The Mendelian inheritance of coat color in mice and in some 
other animals may give an exaggerated idea of the inheritance of 
color in general. That the inheritance is not always of this sort 
seems to be shown by anumber of cases, some of which have been 
given. Pearson’s examination of the inheritance of color in the 
coat of dogs, horses, and of the eye color in man, has led him to 
conclude that in these cases there is no evidence of Mendelian 
inheritance. He points out that when the whole range of the 
ancestry is examined we get more nearly an idea of what the 
color of the offspring will be. For example, in one case, where 
the color of the eye of the mother and of the father was blue, 
only two of the children had blue eyes; but in another case, where 
the father and the mother and all four of the grandparents and 
five recorded grandparents had blue eyes, four children had blue 
eyes. Single cases of this kind in themselves do not show much, 
but these are only samples of what is generally found in many 
cases of the sort. Pearson thinks that the prediction of what 
the color of the eyes is likely to be will be closer when we use the 
ancestry and not the parents alone. If any of these eye colors 
follow the Mendelian rule of dominance and recession, some evi- 
dence of this would appear in the statistics, but nothing of the 
sort has been found.’ It is evident, nevertheless, that these 
cases require careful reéxamination, since there has probably 
been great intermingling of different colors in the past. 
De Vries and some other students of mutation have laid much 
stress upon the immutability of unit characters. De Vries as- 
sumes that transitions between unit characters exist as little as 
between the molecules of chemistry. It cannot be maintained, 
I think, from the evidence that we possess, that unit characters 
are immutable, for there are some cases in which it appears that 
the unit character may be halved by every crossing. It is true 
that some of these cases may be explained by antagonistic char- 
acters both developing and mutually influencing the result; but if 
they do not subsequently separate, it is impossible to tell whether 
or not a new unit character has been formed by combination. 
1“ The Law of Ancestral Heredity,” Biometrica, II, 1903. 
