148 PROBLEMS OF GENETICS 



every student of variation and evolutionary problems should 

 make himself familiar. The two forms with which we are most 

 concerned are known as C. auratus and C. cafer, and are very 

 strikingly different in appearance. In size, proportions, general 

 pattern of colouration, habits, and notes, the two are alike, but 

 the} 7 differ in the following seven respects as stated by Allen. 



Auratus Cafer 



i. Quills yellow. I. Quills red. 



2. Male with a black malar stripe. 2. Male with a red malar stripe. 



3. Adult female with no malar stripe. 3. Adult female with usually a brown 



malar stripe. 



4. A scarlet nuchal crescent in both sexes. 4. No nuchal crescent in either sex. 



5. Throat and fore neck brown. 5. Throat and fore neck grey. 



6. Whole top of head and hind neck 6. Whole top of neck and hind neck 



grey. brown. 



7. General plumage with an olivaceous 7. General plumage with a rufescent 



cast. cast. 



These differences are illustrated in the accompanying coloured 

 plate, which has been most kindly prepared for me under the in- 

 structions of Dr. F. M. Chapman of the American Museum of 

 Natural History. Before going further it is worth considering the 

 nature of these differences a little more closely. All but the last 

 are large differences which no one would overlook even in a hasty 

 glance at the birds. If the only distinction lay in the colour of the 

 quills we might feel fairly sure that auratus was a recessive form 

 of cafer, and so probably it is in this respect. Similarly the black 

 malar stripe of auratus is in all probability recessive to the red 

 malar stripe of cafer and I imagine the pigments concerned are 

 comparable with those in the Gouldian Finch (Poephila gouldiae) 

 of Australia. Both sexes in that species may have the head black, 

 red, or, less often, yellow, and though it is not any longer in 

 question that birds may breed in either plumage, I believe that 

 the young are always black-headed and I imagine that those 

 which become red-headed possess a dominant factor absent from 

 the permanently black-headed birds. 2 Yellow as a recessive 



2 For a case in which a red-headed female X a black-headed male gave a 

 black-headed female and a red-headed male, see Avian Mag., N. S., IV, pp. 49 

 and 329. 



