ON ORNITHOLOGY, 425 
The “Stein”? Eagle varies much in plumage, and in this 
variation age plays an important part; but one transition and 
three main forms of its plumage, and even of its build, can also 
be clearly distinguished, and they are dependent on the loca- 
lity of the nest from which the bird has flown. No stress 
-an_be laid on the very variable size of individuals of all these 
forms, for that is caused by alimentary conditions during the 
youth of the bird. 
The south-west, north-west, and central European ‘“ Stein ”’ 
Hagles may be included in the first group, those of South- 
eastern Hurope in the second, and those that belong to the 
north-eastern and northern parts of the continent in the third; 
while between the second and third groups one finds an 
intermediate, or what may be called a transition form. 
The third form is the Golden Eagle of the old writers Nau- 
mann and Brehm, and so clearly and definitely do these great 
naturalists describe it, that it can easily be recognized. It 
exists, but what to callit, and whether to elevate it to specific 
rank or not to do so, is the point on which the whole question 
hinges. My own opinion is that as an individual species it 
can no longer stand unless two more new species are to be 
created, and then we should have three species of ‘ Stein” 
Eagles. For this the differences are too slight, for they are 
not nearly so important as between Aquila ¢mperzalis and its 
Spanish relative A. adalberti. That is why one speaks of forms 
and not of species, for there is only one species of “ Stein” 
Eagle, but it is split up into three forms according to the 
region in which it lives. As an example of this practice 
with regard to many birds, I may instance the case of Halia- 
étus albicilla. There is a great difference in size between the 
Sea-Eagles of Northern and Southern Hurope, but yet it 
would never occur to any one to make two species out of 
them. 
I have had fewer opportunities of observing the Imperial 
