Introduction: Variation. 7^ 



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 theii- 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. Miiller's Green Parrot, Tanygnathus niuellen, 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 r. luconensis has the head green, which might be taken as an indication 

 of its descent from the green-headed T. muelleri. Is T. miielleri descended from 

 T. luconensis, and T. htconensis 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 what colour 

 the feather is going to become. The adult male of the eastern form of 

 the Blue Rock Thrush, Petropkila cyanus, 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 melanorhyncha, 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. melamrhyncha 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 4 "Wigl eswortli , Birds of Celebes (5Iay.")tli, 1S9S|. '" 



