T4 Osborne on the Coloration of Eggs. 



These examples made me pretty certain that the law applied at 

 least to the Natatores, but I had still the other orders to investi- 

 gate, and, beginning with the Raptores, I made two experiments ; 

 one with an egg of Cathartes aura, in which purple marks changed 

 to reddish-brown, and the other an egg of Accipiter fuscus, in which 

 a very deep purple blotch became a distinct chocolate-brown, sim- 

 ilar to the majority of the markings on the egg. Next turning to 

 the G ' rallatores, I first took an egg of Rallies crepitans, and worked 

 at one of the purple dots until it became a brown similar to the 

 darker dots on the specimen. In an egg of Ibis alba, purple changed 

 to light brown, and in those of jEgialitis meloda and Tringoides 

 macidarius, lilac and purple became dark brown. The Insessores 

 alone now remained for me to work upon, and here the great diffi- 

 culty was in being able to scrape the shell in such a way that, 

 while the outer laj'er of calcareous matter should be removed, the 

 shell should yet remain unbroken. In the case of Corvas ameri- 

 canus this was easy, and light purple became light brown without 

 any difficulty, but when I came to experiment upon the smaller 

 eggs, it was no easy matter to persuade the shell to stay together 

 long enough to give the desired result ; but after quite a number of 

 disasters I obtained very satisfactory results in the cases of Tyran- 

 nus carolinensis, where all the markings became chocolate-brown, 

 in Ampelis cedrorum, where the peculiar purple marks turned to 

 dark brown, and in Agelams phcenicetis, in which purple became 

 almost black. 



These are all the experiments which I have thus far been able to 

 make, and as they comprise all orders of birds, and as the result 

 was uniform in every instance,- it is fair to suppose that, at least, 

 the purple, lilac, and lavender marks on eggs are not the results of 

 corresponding pigments in the oviduct, but are formed merely by 

 the darker pigments covered by a layer of calcareous matter. 



In regard to the brown markings of different shades which occur 

 in very many eggs, the same experiments bring about a rather differ- 

 ent result ; for, while the darker shades seem more fixed, a very little 

 scraping will cause the lighter ones to disappear altogether, show- 

 ing that where the color is light, the layer of coloring matter is thin, 

 and where the color is dark there is always a large deposit ; and I 

 have never seen an egg in which the different shades of brown were 

 not such as a greater or less quantity of tlr> same pigment could 

 produce. 



