492 SUMMARY OF CURRENT RESEARCHES RELATING TO 



has recently had the opportunity of examining a rich material 

 of various coloured egg-shells and of enlarging our knowledge 

 on the colouring matter yielded by them. He distinguishes the 

 following colours differing chemically and spectroscopically from 

 one another : — 1. Oorhodein, already described by Sorby and Lieber- 

 mann ; 2. Biliverdin = Sorby's oocyan, also found by Liebermann ; 

 3. Oochlorin and Ooxanthin, described by Sorby as yellow and red 

 ooxanthin. The other colouring substances found by Sorby 

 Krukenberg could not recognize. 



As regards the dissemination of the different colouring substances 

 amongst the birds, and their distribution in the egg-shells, careful 

 examination led to the conclusion that all flesh-, olive-, or leather- 

 coloured shells, all those which are spotted, sprinkled, or marbled with 

 red, brown, or black, and all spotted or scribbled over with ashy-grey, 

 contain oorhodein, but seldom unmixed with oocyan. It is doubtless 

 universally present. Even in most pale yellowish-brown eggs the 

 oorhodein is not absent. In all green and blue egg-shells there is 

 oocyan. 



In the shells of many closely related species, and even of one and 

 the same species, startling examples are found of the opposing 

 j)resence of both these colouring substances. In many species of 

 birds colour is quite absent in the eggs, and a pure white egg charac- 

 terizes the large family of the Psittacidse. Of the two generally wide- 

 spread colouring substances only one, oorhodein, is entirely absent in 

 the families of the Cursores and Crypturidge, whereas no similar case 

 of absence has been observed with oocyan. 



The representatives of a few families have colouring matters 

 entirely specific to their shells ; thus the Cursores have oochlorin and 

 the Crypturidae ooxanthin. 



The opinion that the colouring substances in all eggs lie on the 

 outer surface is, according to Krukenberg, incorrect. The shells of 

 numerous species of birds are blue throughout, whilst those of some 

 species are perfectly white outside or only coloured brown with 

 oorhodein, but beneath the surface are coloured blue with oocyan. In 

 those coloured with oorhodein the colour never penetrates very deep. 

 A slight wetting of the shell with weak hydrochloric acid removes the 

 colouring matter in many cases, and to remove very dark spots it is 

 only necessary to wet the egg repeatedly with the acid. 



That the oorhodein and oocyan originate from quite different 

 sources, that they are separately fixed on the shell, apparently in 

 different places, as the egg jmsses from the ovary to the cloaca, is 

 verified by the fact that, besides the constant limitation of the red pig- 

 ment to the upper surface, and of the blue generally to the inner 

 substance of the shell, there is always a diffused distribution of oocyan 

 and oochlorin in contradistinction to the oorhodein, which is, without 

 excepliou, more or less circumscribed. 



As tviucal instances of the last assertion are the pencillings on the 

 eggs of the Fringillidte, the red or brownish-black rings on the wide 

 end of many shrikes', woodcocks' and gulls' eggs, and the black and 

 red-brown spots on the eggs of the falcon and thrush. It is generally 



