Problems of genetics / by William Bateson.

  • Bateson, William, 1861-1926.
Date:
1913
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Problems of genetics / by William Bateson. Source: Wellcome Collection.

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    OVERLAPPING FORMS 149 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 dif¬ ferences. When the red crescent is not formed, the feathers which would bear it are exactly like the rest, and no special pigment is visible in them which one can regard as ready to be modified into red. If the crescent is due to a factor it must therefore be supposed that this factor has the power of modifying the pigment of the neck in one special place alone. Dr. W. D. Miller called my attention to the fact that a similar variation occurs in another American woodpecker, the Sapsucker, Sphy- ropicus varius.^ I do not suggest that such variations are without parallel: indeed in P. gouldiae the factor which turns the black of the head into scarlet affects one special region of the black only, being sharply distinct from the unmodified black of the throat. These regions of the head are however often the seat of special colours in birds.'* So also may be instanced the variety of the Common 3 The other variations of this bird are also interesting and important. The normal male has a red head and a red throat. The female has a red head and a white throat, but varieties of the female are known with a black head, thus again illustrating the change from black to red. It should be noted that this is not a mere retention of a juvenile character, but, as the birds mature, the red feathers come up, or as an exception, the black. There is also a western species, ruber, in which both sexes have a great extension of red, and are alike. The male of nuchalis intergrades with this type, but the female does not. ^Dr. W. Brewster, for example, has a remarkable specimen of the Teal {Nettion Carolinense) with a white collar strongly developed at the front and sides of the neck, in a place where the normal has no such mark.