90 
Colouring of the Shells of Birds' Eggs. [January, 
eggs of other species through the kindness of Mr. Osbert 
Salvin, on whose authority I give the various names. 
Taking all the fadts of the case into consideration, it appears 
to me to be almost certain that the redder-coloured consti- 
tuent 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 ex- 
tremely probable. 
No species of Tinamou yet examined contains any recog- 
nisable 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 ohsoleius , C. pileatus , and N othoprocta 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 spedtra of many other eggs 
which appeared at all likely to contain rufous ooxanthine, 
but have not yet seen any fadts which seem to indicate that 
it occurs in any other group of birds than the Tinamous, 
unless, indeed, it be in the case of the eggs of Casuanus 
bennettii and C. australis. If further examination should 
confirm these conclusions, it appears to me that the fadts 
will be of much interest in connedtion with comparative 
physiology, as showing that, to a limited extent, even in the 
case of birds’ eggs, there is a connedtion between the general 
organisation of the animals and their coloured secretions, 
since, as will be seen, such a well-marked group of birds as 
