62 DAVENPORT -DETERMINATION OF DOMINANCE [April 25, 



organ to decide, in many cases, whether a difference is due to a 

 progressive or a retrogressive change. For instance, the long angora 

 coat of rabbits is recessive to short coat ; and this has been cited as 

 a clear case of recessiveness of the advanced condition. But it 

 seems doubtful if such is the case. For the angora coat retains an 

 embryonic quality (viz., of continued growth) which is present in 

 the infancy of the short-haired rabbit and is then inhibited. The 

 inhibiting factor is present in short-haired rabbits and absent in 

 angora rabbits and the presence of the inhibiting factor dominates 

 over its absence. At one time I thought that the dominant white 

 plumage of some poultry was a case of dominance of absence of 

 color. But it now appears that we have among poultry recessive 

 whites which are true albinos, and the dominant whites which must 

 be regarded as " grays," in which pigmentation is obscured by an 

 additional factor like that which turns black hair gray. This gray- 

 ing factor is dominant over its absence. 



It is possible that the future may show that, in accordance with 

 the ideas of deVries, an advanced grade of a character may be 

 regarded as a sum of minute equivalent elementary units ; by the 

 dropping out of these units one at a time a character passes through 

 a series of degradational stages. Then a light brown hair may 

 have one unit of melanic pigment, brown hair two units, dark brown 

 three units, and black hair four units. If this should prove to be 

 true then the four unit condition would dominate over the three 

 unit condition, or the fourth unit would dominate over its absence. 

 But such evidence as I have at present does not favor this view. I 

 am inclined rather to the hypothesis that when the germinal deter- 

 miner of greater intensity meets that of less intensity it dominates 

 over the latter. This hypothesis receives support from another set 

 of facts which go to prove that the idea of varying intensity of a 

 determiner is a true one. This set of facts is derived from the 

 combs of poultry. In one race of poultry — Polish fowl — the comb 

 consists of a pair of horns or broad flaps which lie far back near the 

 base of the beak ; and there is no median comb. In the Minorca and 

 most other fowl there is a single median comb. Now when these 

 two races are crossed we find that the median comb dominates over 

 the absence of median comb; sometimes completely, running in the 



