COLOUR 99 
logical, and can be conveniently expressed by the term Heterochrosis 
(from the Greek érepos and ypécus, 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; when 
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. 
Erythrism, the abnormal occurrence 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 tinctoria, 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, Bufo tinctorius, 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. Wissensch. Berlin, 1882, pp. 
517-524; and a general account by Pelzeln in Verhandl. zool.-bot. 
Gesellsch. Wien, 1865, pp. 911-946. For further information con- 
cerning colours see (Bronn’s) Klassen und Ordn. des Thier-Reichs, 
Vogel, pp. 575-588, and P. Z. 8S. 1882, pp. 409-421, pls. 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 
versd. Kerschner believes (Zeitschr. wiss. Zool. 1886, p. 681) that 
