Introduction; Variation. 
73 
of Celebes may be held to prove the derivation of that species from the blue- 
backed forms of the Oriental Region, and the indications of a wing-band in the 
young Trichoglossm and Psitteuteles of Celebes to demonstrate their descent from 
the banded species of the Australian Region. 
In applying this argument one is apt, however, to stumble on such ditfi- 
culties as the following. Muller’s Green Parrot, Tanygnathus mueUeri, of the 
Celebesian area occasionally displays blue on the head when young, suggesting 
its derivation from the blue-headed T. luconensis of the Philijipines. But the 
young T. luconensis has the head green, which might .be taken as an indication 
of its descent from the green-headed T. muelleri. Is T. muelleri descended from 
T. luconensis, and T. luconensis from a pre-existing green-headed Parrot, or is 
the coloration of the head of the young simply due to some chemical condition 
imposed upon it by the respective parents? 
Mr. Keeler (Evolution Colors Birds 1893, p. 178) has suggested, without 
producing any real proof, that a different colour at the basis of a feather may 
have a phylogenetic value and denote what the colour of the bird at this spot 
was at some period of the past. On the contrary our own obsei rations ha\e 
persuaded us that a different basal colour sometimes shows what colour 
the feather is going to become. The adult male of the eastern foim o 
the Blue Rock Thrush, Petr upkila eg anus, has the breast and abdomen chestnut; 
the immature bird has the feathers of these parts terminally Ringed with whitish, 
next to w'hich is a subterminal bar of dusky, below this usually a little blue, 
and then a large area above the extreme base chestnut the colour which the 
bird will become. Also the jugulum, head and upper parts of the adult are 
blue, but in the young this blue occupies the basal part of the feathers. Not 
the base, but the tip of the feather may sometimes have a phylogenetic 
worth. Evidence of this is shown by the buff- backed Kingfisher of Celebes, 
Pelargopsis melanorhyncha, the young of which by its pale blue back throw's back 
to the other members of the genus, all of w'hich (except another Celebesian 
form) have blue backs. Now the blue in the young P. melanorhyncha is confined 
to the tips of the feathers; below' this they are buff, though there is usually 
also a faint buff fringe round each feather. In the young of this species the 
tendency to change into a form wdth a buff back does not set in in force unti 
the tips of the feathers have already been developed; these tips present t e 
point Avherein it agrees with the rest of the genus — apparently therefore a 
character of long standing, while the buff at the base betrays the character 
which will soon be assumed. 
Hereditary effects of shelter and exposure. — It is proposed here to show 
some evidence drawn from Celebesian birds that modifications of shape or colour 
of feathers as caused by the ever-repeated action of mechanical attrition, or by 
the action of light, are ultimately transmitted to offspring. 
The racket-tail-feathers of Prioniturus. The two middle tail-feathers are 
Meyer & Wigleswortl, Birds of Celebes (May 5th, 1898). 
10 
