2 4 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 Grallatores, 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 AEgialitis meloda and Tringoides 
macularius, 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 layer of calcareous matter should be removed, the 
shell should yet remain unbroken. In the case of Corvus 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 Agelceus pkoeniceus, 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 th^. same pigment could 
produce. 
