Osborne on the Coloration of Eggs. 23 



ON THE COLORATION OF EGGS. 



BY S. D. OSBORNE. 



A short time ago my attention was called to the peculiar appear- 

 ance presented in the markings of certain eggs. I allude more par- 

 ticularly to the purple marks on the eggs of Uria grylle, which 

 have the appearance, mentioned in several descriptions, of being 

 laid on under the surface ; and the idea occurred to me that the 

 purple shade was just such a color as the dark markings of the egg 

 would produce if they were covered with a coating of white, and 

 that therefore it was possible that the bird was provided with only 

 one shade of coloring matter, the varied appearance being given by 

 the manner in which it was deposited. The determination of this 

 point seemed easy : so, taking a knife, and choosing one of the 

 most distinct of the purple marks, I began carefully to scrape it, 

 and in a very short time had reduced the spot to the color of the 

 darker mai'kings on the egg ; thus showing that instead of two dis- 

 tinct pigments, the glands of the oviduct deposit only one, namely, 

 a peculiar blackish-brown. 



Of course, in working up a question of this sort, the first thing 

 to do is to make the observations as general as possible ; and, 

 in the present case, the only way to accomplish this end was by 

 continued experiment. Accordingly, I began with the intention of 

 proceeding with the investigation through all the different orders. 

 The second experiment was with an egg of Alca torda, which I 

 chose as being most similar to that of Uria grylle, and one in 

 which the same result would be most likely to be obtained. As I 

 expected, the apparently purple markings became blackish-brown. 

 I then made a slight deviation and took an egg of Sterna fuligi- 

 nosa, which has a reddish-cream ground-color, over which are spots 

 of a distinct purple, and also of a beautiful shade of reddish-choco- 

 late. It was with some misgivings as to the result that I began 

 to scrape the shell over one of the purple marks, but the effect 

 was instantaneous, and by a very little work I could have made 

 all the mai-kings conform to one color, namely, the chocolate. I 

 then took eggs of Lams argentatus and Sterna macrura, as they 

 were easy to woi'k upon. In both cases the dark purple changed 

 to dark brown. 



