THE OSPREY. 



115 



the yellow area half an inch. More material 

 will be required to ascertain whether or not 

 the chlorochrysotic change observed in this 

 individual went on at the rate normal to the 

 species. 



When in the beg:inning the change was no- 

 ticed, a careful search for pin-feathers was 

 made, without finding a single one. There were 

 many of the intermediate feathers, i^artly 

 green and partly yellow, on the head at that 

 time. In the mitldle of September, when I re- 

 sumed my observations, the moult was just 

 being completed; but where yellow feathers 

 formerly grew, yellow feathers were being de- 

 veloped and where green feathers had been 

 shed, green feathers were being renewed. The 

 importance of this point can not be overrated: 

 for it thus appears that moulting, though it 

 may be concurrent with color change of in- 

 dividual feathers, is not in any way concerned 

 in the latter process, exceiit, of course, in so 

 far as it may substitute for an old, worn-out 

 and inactive feather a new one in which color 

 change may subsequently occur. In one in- 

 stance I observed the change from green to 

 yellow before the feather was fully developed, 

 but no similar cases were subsequentlj' no- 

 ticed. 



This whole matter is one of great intrinsic 

 interest, and probably onlj' one of many very 

 instructive phenomena to be discovered in con- 

 nection with the sadly neglected studj' of 

 feathers. 



The above described facts were confirmed 

 by later tests of their verity, whenever speci- 

 men feathers were pulled from various parts 

 of the head, after the moult had been entirely 

 accomplished. The density of the acquired 

 yellow varies, but according to my observa- 

 tion it is brightest when assumed aptosochro- 

 rnatically — if I may coin the adverb. The 

 golden yellow appears to grow pale as the yel- 

 low parts of the bird extend and are renewed 

 by seasonal moult. 



It is highly probable that aptosochromatism 

 is not confined to C. levaillanti, but that 

 other members of the genus or family may 

 exhibit the same process of color change in- 

 dependent of moult, to a more or less marked 

 degree. The "Single Yellow-head" of the 

 fanciers shows traces of it. and no doubt the 

 peculiar variations in plumage of many Par- 

 rots will afford much curious and valuable in- 

 formation when fully worked out. A singular 

 fact is cited by Gadow (1. c), who states: 

 "In Brazil 'contrafeitos' of the various spe- 

 cies of Chrysotis are fashionable. These are 

 produced by the rubbing in of the cutaneous 

 secretions of a Toad. Bufo tinctorius, into the 

 budding feathers of the head, which then turn 

 out yellow instead of green." 



The principal macroscopic points thus far 

 made may be summed as follows: (1) Change 

 from green to yellow without loss of plumage, 

 or chlorochrys-aptosochromatism. in Chryso- 

 tis levaillanti. is a fact, and a plain one. " (2) 

 Though coincident at times with a moulting 

 process, this color change is entirely inde- 

 pendent of moult, as shown by the presence 

 of changing feathers at all seasons of the 

 year. (3) Eight cases investigated probably 

 show the process to be normal to the species, 

 at least in captivity. (4) In one instance, at 



any rate, the fall moult in no apparent w^y 

 affected the progress of the color change. (5) 

 As shown on the plate, the process is of slow 

 and gradual progress through the individual 

 feather. (6) As far as known, it is independent 

 of age, sex, and season. 



The statements of numberless writers admit 

 dichromatism without hesitation, but they 

 generally fail to say whether or not it is in- 

 dependent of feather loss — that is, aptoso- 

 chromatic. 



It is plainly to be seen, and is well known, 

 that the yellow parts of C. levaillanti increase 

 in area with age, after successive moults, but 

 the chlorochrysotic change of individual 

 feathers, of which I treat, goes on at any age. 



Coloration of feathers is produced in three 

 ways: (a) By chemical pigments which ab- 

 sorb certain light-rays, (b) By objective su- 

 perstructures which modify the pigmentary 

 effects, (c) By subjective structural effects 

 upon the eye, resulting in varying i^rismatic 

 or metallic iridescences, acording to the po- 

 sition in which a feather is viewed. 



The Parrot's color is evidently due to a com- 

 bination of pigments and superstructure, 

 which last is arranged in certain portions of 

 the feather in apparently cellular form. Fol- 

 lowing the simple qualitative tests formulated 

 by Gadow, the pigments known as zoomelauin 

 and zoonerythrin were readily determined, 

 but the results for zooxanthin were not so 

 successful, though this latter pigment proba- 

 bly constitutes a large portion of the coloring 

 matter of the feather. In a green feather of 

 the head the red and black combined formed 

 a dense mass at the tips of the barbules, ex- 

 tending downward for about two-thirds of the 

 length of these parts; there was a central col- 

 umn of the same down the liarbs, appearing 

 brownish under the microscope when unsec- 

 tionized (an effect due to the surrounding yel- 

 low parts); and a heavy mass of dark matter 

 was present at the base of the rhachis near 

 the junction of the calamtis. in the form of a 

 long cone with a bifurcated base; the body of 

 this dark cone gradually tapering up the 

 rhachis till it ended in a fine point about half 

 way up the length of the feather. The space 

 intervening between this cone and the walls 

 of the rhachis, together v\7fh the rest of the 

 shaft, was filled with fine granules of appar- 

 ently the same varieties of pigments, some- 

 times in rod-shaped masses, giving a very curi- 

 ous apjjearance. This effect is also produced 

 at the junction of the barbs with the rhachis. 

 The yellow pigment is fotind as a diffuse non- 

 granular stain in the lower portions of the 

 barbules. and surrounding the well-defined 

 central portions of the barbs. By transmit- 

 ted lig-ht such a feather appears of the com- 

 bination coloring of the underlying pigments, 

 and a dull yellowish gray results. When 

 crushed, a similar effect is obtained. This is 

 in itself suggestive of a structural element in 

 the coloring properties, which, as will be pres- 

 ently shown, is involved in the centrally-.sit- 

 nated cellular pigment masses. This agrees 

 with Gadow's statement that in the genus 

 Chrysotis. "the surface of the radii and rami 

 fbarbules and barbs) is smooth and quite 

 transparent, while between it and the pigment 

 Is a layer of small polygonal bodies." 



