OCR Text |
Show 1875.] COLOURING O F BIRDS' EGGS. 361 the shell of such redder Tinamou-eggs as those of Crypturus obsole-tus (Wickham), absorbs the blue, the green, and some of the yellow rays, but transmits the orange and red; so that the colour is a sort of orange-red, made duller and of more leaden tint in the eggs of other species by mixture with oocyan. The result is that we obtain tints which are not so decidedly different from those due to a mixture of oocyan with oorhodeine as to lead any one to conclude at once that they were not due to the same substances. However, when the eggs in their natural state are properly illuminated by light so condensed on them sideways from a lamp that as little as possible is reflected from the surface, the spectra are seen to differ entirely. When oorhodeine is present, one or more of its absorption-bands may be seen ; but when the red colour is due to rufous ooxanthine, no trace of any such bands can be recognized. M y knowledge of the chemical and optical characters of rufous ooxanthine when in a state of solution were derived from the study of the eggs of the rufous Tinamou (Rhynchotis rufescens)• and hitherto I have been able to study only the spectra of the eggs of other species through the kindness of Mr. Osbert Salvin, on whose authority I give the various names. Taking all the facts of the case into consideration, it appears to me to be almost certain that the redder-coloured constituent in all the different species is rufous ooxanthine. At all events, none show any trace of the bands of oorhodeine, and all show the same absorption of light of less wave-length than about 590 millionths of a millimetre.. All that remains to be done to make this point certain is to examine the solutions derived from other species than that I have named, in order to be sure that the chemical as well as the optical characters are identical. In the present state of the question the following conclusions must be looked upon as only extremely probable. No species of Tinamou yet examined contains any recognizable amount of oorhodeine. The colour of many species is due to a variable mixture of rufous ooxanthine with oocyan, the former greatly preponderating in such red eggs as those of Crypturus obso-letus, C. pileatus, and Nothoprocta curvirostris. The red and blue constituents occur in more equal proportion in the peculiar lead-coloured eggs of Rhynchotis rufescens. Calodromas elegans, when in a comparatively fresh state, contains so much yellow ooxanthine that it is pale green-yellow; but by exposure to light this yellow constituent is decomposed, and the shell becomes a pale flesh-colour from the small residual amount of rufous ooxanthine. Fresh-laid eggs of Tinamus solitarius are of nearly the same deep green as those of the E m u ; and the long-kept eggs of Tinamus robustus are of fine blue, as though in some species there were very little rufous ooxanthine, and the colouring, as in the case of the Emu, due to a mixture of oocyan and yellow ooxanthine. It will thus be seen that all the various peculiar tints can be explained by the presence of a variable quantity of rufous ooxanthine. I have carefully examined the spectra of many other eggs which appeared at all likely to contain rufous ooxanthine, but have not yet |