56 
Introduction: Variation. 
dichromatism among Celebesian birds is afforded by the Heron, Demiegretta sacra; 
this bird is ordinarily slate-coloured, but a pure white form is very frequent, 
and in some parts of its range, as in the Andamans, white individuals number 
some 20 per cent of the species. The two forms are known to breed together, 
and white young ones, as well as the usual dark ones, are known from 
the nest; piebald specimens are also not uncommon. It may well be, as has 
been suggested by Dr. Stejneger, that Demiegretta sacra will in the end be- 
come a pure white species, like the allied Herons of the genus Herodias, one 
of Ardea, and Buhidcus (when not breeding). In other parts of the world three 
more Herons are known among which white individuals are of very frequent 
occurrence (see text, p. 822). 
The genus Spilornis is supposed by some ornithologists to be dichromatic 
when young, but further proof of this is wanting (see p. 3). Ardetta eurliythma 
perhaps makes an approach to dichromatism, since the male is sometimes known 
to breed in its immature dress (the ordinary female dress), and a female is 
occasionally found in the male plumage. Other cases of dichromatism have 
not been found among Celebesian birds, and the phenomenon is indeed always 
rare in ornithology. 
Modifications of the individual due to foreign viole7ice, such as injuries to feathers 
and parts of the hody^ disease, effects of shelter and exposure, of food etc. cannot 
be discussed here, as leading too far. Only a remark or two. The heredity of 
oft-repeated external action on feathers is discussed below, pp. 73 — 79. Remark- 
able effects may sometimes be produced by food, such as the conversion of 
Canaries or white Fowls into red ones by feeding them with Cayenne pepper. 
Isabelline-coloured Pigeons fed with crumbs coloured with Methyleosine were 
turned into birds of a permanent red tint, and green Australian Parrakeets 
[Mellopsittaciis] supplied with millet coloured with Methylviolet were converted 
into blue birds, the yellow forehead becoming white or dirty white (Sauermann, 
Mitth. Ornith. Vereins Wien 1890, pp. 92 — 94). Parrots {Sittace) in Brasil are 
made to change colour into yellow by plucking out feathers and inoculating 
the wounds with a frog’s or toad’s blood or with the milky secretion from its 
skin; when the new feathers grow the colour is changed. The common 
Amazonian green Parrot {Ckrysotis), if fed with the fat of large Siluroid fishes, 
becomes beautifully variegated with red and yellow feathers. In Halmahera 
Lorius garrulus is said to be influenced in a similar manner. (After v. Martins 
and Wallace, communicated by Meyer: Sitzb. Ak. Wiss. Berlin 1882, 521.) 
Thus we imagine that a bird flying to a neighbouring island and finding 
there another sort of food, may, if settled there, acquire some new character in 
coloration; e. g. Loriculus stigmatus flying over to Banggai becomes sclateri ruber, 
to Togian Island quadncolor, etc. etc., these forms only differing slightly. Such 
alterations may occur per saltum or at least quickly, not requiring generations. 
A fruit from Batavia planted at Manado does not always remain the same, as 
