308 The Egg of Thalassidroma Leachii, etc. 
closely resembling it, that a careless eye might never note thé 
difference. Both birds are apparently alike in habit, food, 
nesting, and strongly alike also in external. appearances. 
Why should they not also dwell together in the same places? 
No law of nature is apparently more fixed than this ; but why 
it is so is one of the many inscrutable facts, which, the more 
we seek to understand, the less are we able to explain them. 
Arr. lI. — Notice of the Egg of Thalassidroma Leachit, 
with Descriptions of the Eggs of Procellaria Bulwerii, 
Procellaria obscura, and Puffinus major. Read before 
the Boston: Society of Natural History. By T. M. Brew- 
ER, i 
Ix the paper which I read a few weeks since, I referred to 
the marked difference’ in size between the specimens of the 
eggs of the Forked-tailed Petrel obtained in the Bay of 
Fundy, and one given me as a European specimen of the 
same. It suggested the possibility of specific differences 
which seemed worth investigating. Since then I have re- 
ceived information which convinces me that there is no real 
difference between the eggs of the European and the Ameri- 
can bitds, and that the egg given me, in the’ first instance, 
and referred to in my paper as that of Leach’s Petrel, is not 
the egg of that bird, but of a smaller species. The day after 
my communication was: read I received a letter from a cor- 
ie oen in Manchester, England, to whom I had sent a 
^n of the American egg, and had mentioned my sus- 
jicion ot the possible existence of specific differences between 
the birds of the two continents. He wrote me in reply, that 
. it corresponded exactly in size with the European specimen in 
. his cabinet. Since then I have received from another corres- 
