Other Kmds 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, 

 i.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- 

 Hshed 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. 



