SINGLE-COMB MINORCA AND WHITE-CRESTED POLISH. 



13 



cases in which the records read three- fourths high ; but even in the PoUsh 

 fowl the high nostril varies somewhat. Theoretically, we should expect 25 

 per cent of the second generation to have the recessive high nostril. The 

 deficiency may indicate merely insufficient numbers, or perhaps some of 

 the " one-half high " group truly belong in " class 3." The essential facts 

 are, first, that high and narrow are segregated, and that in the second 

 generation also dominance is frequently imperfect. 



First generatioyi hybrid crossed "with Minorca. The heterozygous mothers all 

 had narrow nostrils, as of course had the Minorca father. No true case of 

 high nostril occurred. The recorded distribution is as follows : 



It seems probable that the 1 2 individuals with narrow nostrils belong to 

 homogametous birds and the 13 individuals of class 2 to heterogametous 

 birds. 



3. Cerebral Hernia. — First hybrid generation. Every bird was without a 

 typical cerebral hernia. Nevertheless some of them showed clear traces of 

 their mixed ancestry. On the frontal bone of all fowl is the so-called 

 frontal eminence which is covered by fascia and the thickened skin of the 

 crest. The profile of the skull from the apex of this eminence to the 

 parietal is nearly straight, except for a slight concavity limiting the frontal 

 eminence. In hybrids this concavity is frequently still more marked, the 

 eminence being higher. Indeed, in one case (No. 405 9 ) the concavity is 

 so marked that, as far as one can judge from the living bird, there is a 

 slight hernia. We see, then, that though plain head is dominant it is incom- 

 pletely so. 



Second hybrid generation. The following is the distribution of this char- 

 acteristic when the hybrids are bred i7iter se. Expectation is: 75 per cent 

 without hernia, 25 per cent with hernia. The result agrees closely with 

 expectation. 



Characteristic. 



Hernia absent. 

 Hernia present 



Total .. 



Frequency. 



75 

 23 



98 



Per cent. 



76.5 



23-5 



lOO.O 



First hybrid generation crossed with Minorca. Since the first generation is 

 DR and Minorca is D, half of the offspring will be pure dominants and half 



