MUSCICAPINjE. 
109 
tainly none more inexplicable, than that certain 
groups of birds, haring a limited geographic distri- 
bution, should be distinguished from others of the 
same family (but inhabiting another continent), hy 
a slight but invariable deviation in the form of their 
wings. This difference might be accounted for, if, 
upon further investigation, we had found that it was 
accompanied by a difference in the mode of flying 
or of capturing the food. But hitherto not the 
slightest variation has been detected, on these 
points, between the fly-catchers ( Muscicapa ) of 
the Old "World and those of America. Neverthe- 
less, so decidedly different is the structure of the 
wing in these two great geographic groups, that we 
may at once decide from this circumstance alone, 
whether a species we see for the first time is a New 
or an Old World fly-catcher. We drew the atten- 
tion of ornithologists to this remarkable fact some 
years ago*, and subsequent experience has not fur- 
nished us with a single exception to the rule. The 
common grey fly-catcher of Britain catches its prey 
in precisely the same manner, so far as 1 can dis- 
cover, as do the little tyrants ( Tyrannula ) of Bra- 
zil, hoth sit upon a twig, dart at passing insects, and 
return to the same station ; but the European 
species has the first quill-feather so small as to be 
spurious, or as it were elementary, while that of the 
other is three times as long, and the proportions of 
* Northern Zoology. 
