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. 4 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. 



4 Dr. W. Brewster, for example, has a remarkable specimen of the Teal (Ncttion 

 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. 



