1875.] COLOURING OF 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 mix- 
ture 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 ooxan- 
thine, no trace of any such bands can be recognized. My know- 
ledge 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 con- 
sideration, 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 soluéions derived from other 
species than that I have named, in order to be sure that the chemi- 
cal 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 Emu; 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 
