406 



Scientific Proceedings, Royal Dublin Society. 



though split in two. Thus the Breda comb carried either factors that were 

 recessive to x and v/, or the factors x and y themselves. The first crosses of 

 the Breda and single mating were not mated again, and so no second crosses 

 were produced by which this point could be decided. 



But from the rose and Breda matings, half the doubt can be decided. 

 There were single combs in the second crosses. Where did they come from ? 

 The constitution of the rose parent was XXyyCCss, and of the Breda, so far 

 as yet known, vcDD. From these a single comb, whose constitution we 

 know to be xxyyGCss, was bred. The factor xx was not contained by the rose- 

 combed parent, and must therefore have been carried and brought in by the 

 Breda, whose constitution, therefore, must be at least xxvvBD. As to whether 

 it also contains yy, there is uo direct proof ; but the fact that it contains wx, 

 together with the further fact that its progeny when mated with the 

 single comb are apparently different in no way from single, except in duplicity, 

 is very strong presumptive evidence that it does. If a mere opinion were 

 expressed, it would be that the constitution of the Breda comb is xxyyvvDB. 

 The matter cannot be settled absolutely until second crosses are bred from 

 Breda with pure pea or walnut, neither of which contains yy. 



It may be pointed out, however, that there is further presumptive 

 evidence in support of the above opinion. If it be correct, the constitutions 

 of all tlie combs discussed should be at least when pure :— 



. XX y y CO 

 . XX yy 

 . XX YY 

 . XX YY CO 



, XX y y V V 



The rose oomb and the Breda were crossed, 

 constitution of the Breda, as given in the above table, is correct, then the rose 

 and Breda differ in three pairs of characters ; and, in their second crosses, 

 there should be eight groups with the usual numbers in each, and with the 

 pure individuals showing these constitutions : — 



Single 



Rose 



Pea 



Walnut 



Breda 



CO 

 CO 



s s. 

 s s. 

 s s. 

 s s. 

 DD. 



On the assumption that the 



