1. Quills _yellow_. 1. Quills _red_. 2. Male with a _black_ malar 2. Male with a _red_ stripe. malar stripe. 3. Adult female with _no_ 3. Adult female with usually a malar stripe. brown malar stripe. 4. _A scarlet nuchal crescent 4. No nuchal crescent in in both sexes._ either sex. 5. Throat and fore neck 5. Throat and fore neck _brown_. _grey_. 6. Whole top of head and hind neck 6. Whole top of neck and hind _grey_. neck _brown_. 7. General plumage with an 7. General plumage with a _olivaceous_ cast. _rufescent_ cast. These differences are illustrated in the accompanying coloured plate, which has been most kindly prepared for me under the instructions 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 form of a red is certainly very common, but red and black as variants of the same pigment are less usual. In the Gouldian Finch we seem to have a case where a pigment can assume all three forms. It would be interesting to know whether the red of the malar stripes in _Colaptes_ is a pigment of the same nature as the red of the quills. Both in _Colaptes_ and in _Poephila gouldiae_ I have seen specimens intermediate between the black and the red, and the appearance of the part affected was exactly alike in the two cases, red feathers coming up among the black ones, and many feathers containing both red and black pigments mixed together. The development of the scarlet nuchal crescent in _auratus_ and the absence of this conspicuous mark in _cafer_ constitute from the physiological point of view the most remarkable pair of differences. When the red crescent is not formed, the feathers which would bear it are exactly like the rest, and no special