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 Trichoglossus 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 diffi- 
culties as the following. Muller’s Green Parrot, Tanygnathus muelleri^ of the 
Celebesian area occasionally displays blue on the head when young, suggesting 
its derivation from the blue-headed T. luconensis of the Philippines. But the 
young T. liicone7isis 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 observations have 
persuaded us that a different basal colour sometimes shows w^hat colour 
the feather is going to become. The adult male of the eastern form of 
the Blue Rock Thrush, Petrophila cganus^ has the breast and abdomen chestnut; 
the immature bird has the feathers of these parts terminally fringed with whitish, 
next to which 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 melanorhgncha, the young of which by its pale blue back throws back 
to the other members of the genus, all of which (except another Celebesian 
form) have blue backs. Now the blue in the young P. melanorhgncha 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 with a buff back does not set in in force until 
the tips of the feathers have already been developed; these tips present the 
point wherein 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 & Wigl esw o r th, Birds of Celebes (May 5th, 1898). 
10 
