258 
COLOUR IN NATURE 
CHAP. 
4. Yellow ooxanthine—a bright yellow pigment giving rise 
when mixed with oocyan to the bright permanent 
green so familiar in the eggs of the emu. 
5. Rufous ooxanthine—a reddish-yellow pigment perhaps 
peculiar to the eggs of the tinamou. 
6. A substance giving a banded spectrum but otherwise 
little known. 
7. Lichenoxanthine—a brick-red pigment, possibly due to 
the growth of minute fungi. 
As to the nature of the pigments, Krukenberg 
regards the blue and green colours as due to modi¬ 
fications of the bile - pigment biliverdin, and the 
brown and red colouring-matters as closely allied to 
iron-free hmmatin (hsematoporphyrin). A more recent 
observer, Wickmann, regards all the pigments as 
originating directly from haemoglobin. According 
to him, the pigments originate from the blood which 
fills up the corpus luteum. This blood stagnates 
and undergoes retrogressive metamorphoses which 
result in the formation of the pigments. He com¬ 
pares the process to that occurring in mammals, 
where there is a formation of haematoidin crystals in 
the corpus luteum; the difference may, perhaps, be 
explained by the diminished outflow of blood in 
mammals consequent on the greatly reduced size of 
the ova. According to Wickmann, the pigments 
formed in this way within the ovary are shed into 
the oviduct, and mingled with the materials of the 
shell in its uterine portion. If his observations are 
correct, they perhaps help to explain the facts noticed 
by Professor Newton (op. cit ), that when a bird lays 
only two eggs, it not infrequently happens that all the 
available pigment is deposited on one, while the other 
may be colourless. Professor Newton gives the Golden 
