Wilson — Unsound Mendelian Developments. 405 



factor by D, and the simplicity factor by s, the factorial constitutions of 

 pure rose and pure single, so far as we now know them, may be written 

 down in the customary manner as XXyijss, and xxi/ysa. 



But the matings with the Breda comb show anotlier pair of factors. Tiie 

 rose and single combs are both of some size, while the Breda comb is merely 

 a vestige ; and the first crosses of the two former with tlie Breda are also of 

 some size. Thus, tlie rose and single combs each carry a factor which allows 

 or causes to be produced a comb of some size, while the Breda carries a 

 factor whicli is responsible for nothing but the vestige of a comb ; and, since 

 the first crosses are of the size of rose and single, the size factor is dominant 

 to the vestige factor. Then, if we represent the former by C, and the latter 

 by V, the constitutions of pure rose and single combs should now be written 

 down XXijtjssCC, and xxyyssGG. 



From the same matings the constitution of tlie Breda comb can also be 

 found. We have seen already that it contains D and v. It can also be 

 shown to contain x and y. Let us go back to the typical examples chosen 

 from cattle. In the third example from cattle differing in three pairs of 

 characters, tliere were a group black, polled, and white-faced, and another 

 red, horned, and normal-faced. But these two groups had many other 

 characters besides — how many we do not know — in none of which they 

 differed. The characters of these two groups may therefore be written down 



B P W p q r in the one case, and 



r h n p q r in the other. 



Some of the characters pqr are dominant, some recessive to other 



characters in other cattle ; but most of them are the same as in other cattle. 



There can be no doubt, however, that pqr are common to both the 



above groups, else their second crosses would have differed in more tlian 

 three pairs of characters. Thus it must not be assumed that, when two 

 groups differ in one or more pairs, they have no other characters than those 

 in which they differ. If one group is dominant to another in the way the 

 rose comb is dominant to the single, it must not be assumed that the two 

 groups are each the result of only one factor : that they have no other factors. 

 The real state of affairs is that they may have many others, but, when 

 suflScient crossing brings out no differences, these others (so far as they are 

 mateable) are the same for both groups. 



When the Breda comb was mated with the single, the first cross was a 

 split or duplex single comb. The factor for duplicity had effect, but the 

 vestigial factor had no apparent effect. The factors x and y of the single 

 comb also had effect, since the result was still what we call a single comb 



