1876.] Colouring of the Shells of Birds' Eggs. 93 
its spedlra and those of oorhodeine occurs when they are 
both dissolved in the same solvent. It is more analogous 
to the connection between the two kinds of haemoglobin, 
described in my paper on the evolution of that substance, 
published in the current number of the “ Quarterly Journal 
of Microscopical Science,” which can be proved to contain 
the same haematin united with a different albumenoid. 
In order to show the nature of the relation of the speCtra, 
I subjoin the following tables, giving the position of the 
centres of the absorption-bands in millionths of a millimetre 
of wave-length. 
Table i. — Dissolved in nearly neutral Alcohol. 
Oorhodeine .... 630 602 578 539 504 
Cruentine 623 596 572 534 500 
Difference . . 7 6 6 5 4 
Table 2. — Dissolved in Alcohol with strong Acid . 
Oorhodeine . . . 604 580 557 
Cruentine .... 598 574 552 
Difference . . 6 6 5 
Though I feel much tempted to enter further into the 
purely physical part of the question, it will, I think, be 
better to confine myself to what bears more diredlly on 
zoological fadts. According, then, to the above-described 
general principles, these fadts lead us to conclude that 
oorhodeine is in some way or other closely related to 
cruentine, but not identical with it, as shown not only by 
the well-marked difference in the spedtra, but also by the 
difference in their solubility and power of resisting the 
decomposing adtion of powerful reagents. 
In the present state of our knowledge the most plausible 
explanation of all the fadts is that perhaps oorhodeine and 
cruentine contain some common coloured radical of the same 
chemical or physical constitution, combined with some other 
substance which is itself colourless, and that this second 
constituent is not the same in oorhodeine as in cruentine, 
but differs sufficiently to modify the general properties and 
to slightly alter the size of the ultimate molecules, so as to 
cause them to be related to waves of light of a little different 
length. Assuming this principle to be true, the fadts 
lead to the conclusion that the oorhodeine of birds’ eggs is 
derived from the red colouring-matter of the blood, not by 
