REPRODUCTION— CONCERNING EGGS 199 



6. ^ — a pigment giving a banded spectrum 



but otherwise little known. 



7. Lichen ooxanthine — a brick-red pigment, possibly due to 



the growth of minute fungi. 



In some respects we must regard Lichen ooxanthine as the 

 most remarkable of all, that is, if it is really of fungoid origin. 

 This pigment, it seems, occurs in almost all kinds of plants, but 

 especially in lichen and fungi. Dr. Sorby, however, believed 

 that it is a normal constituent of the shell of eggs having a 

 peculiar brick-red colour. Some of the most valuable work in 

 recent years on the nature of the pigments of animals has been 

 done by Miss Newbigin — to whom, and to Professor Newton, 

 we are indebted for this summary — but she has apparently not 

 yet investigated the' point. 



The other pigments here mentioned are apparently blood 

 secretions, derivatives of haemoglobin. According to Wickmann 

 they originate from the blood which contributes to the formation 

 of the corpus luteum, the " yellow body " which is formed by the 

 escape of blood from the capsule in which the egg is formed, 

 after the expulsion of the egg. This " yellow body " appears 

 later to undergo decomposition, or rather a retrogressive meta- 

 morphosis, which results in the formation of pigments. These 

 pigments thus formed within the ovary are shed, according to 

 Wickmann, into the oviduct and mingled with the materials of 

 the shell in its uterine portion, the varying and characteristic 

 hues being due to the difference in the composition of the blood 

 in each particular species. 



That these pigments are blood-pigments rather than bile- 

 pigments is more than probable, but it is open to question 

 whether they are derived and disposed of in the manner sug- 

 gested by Wickmann ; rather, if they are really derived from the 

 corpus luteum, it would seem that the products of the meta- 

 morphosis must be absorbed and redeposited in the tissues of the 

 oviduct, where they become set free after the shell has reached 

 a somewhat advanced stage of development; and for the 

 following reasons : '' If a bird," says Professor Newton, " bear- 

 ing in its oviduct a fully formed egg, be captured, that egg will 

 speedily be laid under any circumstances of inconvenience to 

 which its producer shall be subjected, but such an egg is usually 



