85 
i 8 j 6 .] Colouring of the Shells of Birds' Eggs. 
since, as will be apparent from what I have already said, 
when the carbonate of lime is dissolved out by a weak acid 
the whole of the oocyan disappears if the amount of yellow 
ooxanthine is considerable, whereas no such decomposition 
occurs when it is absent. Rufous ooxanthine also differs 
from yellow ooxanthine in absorbing light to a very con- 
siderably greater distance from the blue end. Even when 
dissolved in alcohol it absorbs not only all the blue, but also 
at least one-half of the green ; that is to say, all light of less 
wave-length than 550 millionths of a millimetre is absorbed, 
and all of greater wave-length transmitted, which, of course, 
is a very well-marked difference, as will be seen on compar- 
ing the spedtra given in fig. 3. 
Fig. 3. 
700 400 
Yellow ooxan- 
thine. 
Rufous ooxan- 
thine in solu- 
tion. 
Rufous ooxan 
thine in a 
solid state. 
Spettra of the Ooxanthines. 
When in a solid state in the egg the absorption extends 
considerably further towards the red end, down to wave- 
length 590 or thereabouts ; so that the tint is decidedly red, 
and not the orange-colour of the solution or the bright 
yellow of yellow ooxanthine. When mixed with oocyan, it 
therefore gives rise to the peculiar lead-colour of the eggs of 
the rufous Tinamou — and not to green, like that of the fresh 
eggs of the Emu. 
6. Substance giving narrow absorption-bands in the red.— 
Unfortunately I have not yet succeeded in obtaining this in 
sufficient quantity, or sufficiently free from other substances, 
to be able to decide whether its true colour is blue, green, or 
brown ; but the fadt of its giving a spedtrum with several 
narrow absorption-bands in the red would certainly indicate 
that, when mixed with other colouring-matters, it would 
cause them to have an abnormally browner tint. Small 
quantities of it occur in very many eggs ; but I have not yet 
found it so abundant in any as to exercise a more important 
