Other Kinds of Hybridizing 169 
laws as general, the results suggest certain questions of great 
theoretical importance. 
For instance, the results seem to me to indicate that we are 
dealing not with a question of partial purity of the germ-cells, 
but with the question of the relation of dominance and recessive- 
ness of contrasted characters. In the first generation there can 
be no doubt that both characters are present. In the first 
class of cases the activity of one character completely suppresses 
the activity of the other — the characters are mutually exclusive, 
z.e. the development of one suppresses the development of the 
other. In the second class of cases both characters may become 
active either at the same time in the same cell, producing blend- 
ing; or in different parts of the soma, —different cells or groups 
of cells, —producing a mosaic or a piebald condition. 
If, then, the same condition holds in the second generation, 
the most probable conclusion is, I think, that there has really 
been no separation of the contrasted characters in the germ-cells, 
but only a condition of relative dominance and latency estab- 
lished that is akin to but not identical with the dominance and 
recession in the first generation. Such a.conclusion seems to 
me more in conformity with the results than that which tries to 
explain the facts of the second class as due to imperfect separation 
in the germ-cells of the two contrasted characters; for on my view 
the results in the first and second generation are accounted for on 
the same assumption; while in the current interpretation it is not 
apparent why imperfect separation in the germ-cell of F, should 
not occur as often in the first class of cases as in the second. 
In the preceding pages the heredity of a large number of char- 
acters of domesticated animals has been described. Relatively 
few facts regarding wild species have been given. The objec- 
tion has sometimes been raised that our domesticated animals 
are contaminated to such an extent by crossing that they offer 
questionable material for studies in heredity, and that the study 
of wild forms is more profitable. This objection is misleading, 
since it directs attention away from the point at issue and rests 
on several false or questionable assumptions. 
