5^ 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, -nhite individuals number 

 some 20 per cent of the species. The two forms are known to breed together, 

 and pure 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 Bubulctis (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 eurhythma 

 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 violence, such as injuries to feathers 

 and parts of the bodg, 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 

 [Mellopsittacus] supplied with millet coloured with jMethylviolet were converted 

 into blue birds, the yellow forehead becoming white or dirty white (Sauermann, 

 Mitth. Ornith. A'ereins 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 Chri/sotis), 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. Marti us 

 and Wallace, communicated by Meyer: Sitzb. Ak. Wiss. Berlin 18S2, 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 stigmatiis fiying over to Banggai becomes sclateri ruber, 

 to Togian Island quadricolor, 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 



