COLOUR 99 



logical, and can be conveniently expressed by the term Heterochrosk 

 (from the Greek erepos and ;^paio-tSj colouring). The following are 

 the chief cases : — 



Albinism, caused by the pathological absence of the black pig- 

 ment, and often locally produced by a lesion of the pulp of the 

 growing feather ; extreme instances are white Ravens and Black- 

 birds. 



Melanism, produced by the superabundance of black pigment, 

 mostly causing the feathers to assume a darker or more sooty colour. 

 Melanistic specimens have been described of many birds, such as 

 Bullfinch, Skylark, and in particular of the common Snipe, which 

 in this phase has by some been regarded as a distinct species, 

 Scolopax sabinii. 



Xanthochroism, mostly in originally red or orange feathers ; Avhen 

 the feathers are yellow instead of green, this may possibly be a 

 reversional step or a case of arrested development because of the 

 absence of the green-making superstructure. 



Erytlirism, the abnormal occuiTcnce of red, mostly confined to 

 originally yellow or orange feathers, occasionally produced by 

 abnormal food, like cayenne pepper, or directly by the colouring 

 matter of Rubia tindoria, one of the madder -worts. A certain 

 correlation between green and red is exhibited by the intensely 

 green adult males of Eclectus polychlorus, the females being bright 

 red and the young of both sexes being reddish, without any 

 indication of green in the young male. 



In Brazil " contrafeitos" of the various species of Chrysotis are 

 fashionable. These are produced by the rubbing in of the cutaneous 

 secretion of a Toad, Bnfo tindorius, into the budding feathers of 

 the head, which then turn out yellow instead of green. 



Concerning the literature of Albinism and Melanism the reader 

 may consult Toppan, Bull. Ridgway Club, 1887, pp. 61-77, and 

 Deane, Bull. Nuttall Orn. Club, 1876, pp. 20-24; "Xanthochroism" 

 in Parrots: Meyer, Sitzber. k. Akad. JFissensch. Berlin, 1882, pp. 

 517-524; and a general account by Pelzeln in Verhandl. zool.-bot 

 Gesellsch. Wien, 1865, pp. 911-946. For fui^ther information con- 

 cerning colours see (Bronn's) Klassen und Ordn. des Thier-Reichs, 

 Vogel, pp. 575-588, and P. Z. S. 1882, pp. 409-421, pis. 27, 28. 



The distribution of colour in the feathers and the colour-pattern 

 of the plumage require some notice. 



It is a hitherto unsettled question if the longitudinally striated 

 or the crossbarred feathers are the older style of coloration. 

 The general impression of the coloration of a bird is the sum 

 total of the coloration of all the uncovered parts of the feathers. 

 This sounds like a truism, but means that crossbarred feathers 

 can never give the general impression of a striated plumage and vice 

 versa. Kerschner believes (Zeitschr. wiss. Zool. 1886, p. 681) that 



