1876.] 
8 9 
Colouring of the Shells of Birds' Eggs . 
vegetal chromatology.* There is also reason to suspedt a 
connexion between the evolution of one colouring-matter 
from another, or from colourless constituents, and the pro- 
gress of the general organisation. These fadts naturally led 
me to consider whether any such connection could be recog- 
nised in the case of birds' eggs. Much remains to be learned 
before any positive opinion can be expressed ; but what is 
already known appears to be sufficient to prove that, if there 
be any definite connection between the general organisation of 
birds and the coloured substances found in their eggs, it is not 
of such a kind as is at all obvious to any one who, like myself, 
is not thoroughly acquainted with anatomical details. Six 
out of the eight different colouring-matters occur in variable 
amount in a very great variety of eggs, but there is no greater 
variation than is met with in the different individual eggs of 
the common Guillemot ; so that the study of the colouring- 
matters cannot be looked upon as of any value in distin- 
guishing species, or even much wider groups, except, 
perhaps, in one particular instance. Hitherto I have met 
with rufous ooxanthine only in the eggs of the Tinamous, 
and perhaps in those of some species of Cassowary ; and 
though the question needs further examination, it is desirable 
to give a short account of what is already known. 
As previously described, rufous ooxanthine when in solid 
form in the shell of such redder Tinamou-eggs as those of 
Cvyptums ohsoletus (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 withoorhodeine as to lead any one to con- 
clude 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 spedtra 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 recognised. My 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 spedtra of the 
1 
^Proceedings of the Royal Society, vol. xxi., p. 442. 
VOL. VI. (N.S.) 
N 
