2 INTRODUCTION. 
It is true that a few island forms may not come very exactly 
under this definition, but in these cases the differences are such 
as are obviously parallel to those obtaining in non-isolated areas 
on the mainland. Where evolution and isolation have evolved 
forms which are definitely divided from all others by some 
characteristic which is not one merely of degree, I have treated 
thei as distinct species. 
In India we are constantly meeting with the most intricate 
cases of subspecific variation, and a study of birds which admits 
the recognition of these geographical races and the wisdom of 
naming them affords infinitely greater interest both to the field 
and to the scientifie worker than does the easier method of 
lumping them all together. For instance, to take two of our 
most common birds, the Indian House-Crow and the Red-vented 
Bulbul. Two species of the former aud many of the latter have 
been recognized and given specific names, although the differ- 
ences between them are in no way specific and are not any 
greater than the differences which exist in many other forms 
which have been left undivided. 
The second point to which reference must be made is the 
unfortunate necessity which has arisen for very numerous 
corrections in Oates’ nomenclature. Such corrections cannot but 
be a source of some difficulty to the older race of field naturalists, 
and students who have learnt these names will now have to learn 
those which replace them. The younger generation will, how- 
ever, have the satisfaction of knowing that they are learning 
names which, with few exceptions, will be permanent; for, with 
strict adherence to the laws of priority, a time will soon come 
when we shall really have arrived at the bed-rock of nomen- 
clatorial research. It should ve mentioned here that I have had 
the unstinted help of Mr. Tom Iredale in this particular branch 
of the work, and his unrivalled knowledge of bibliography and 
nomenclature has been of inestimable help to me. 
Another difference between this and the preceding edition will 
also be noted. With the approval of the editor, Sir Arthur E. 
Shipley, the synonymy has been reduced to references to the 
original description and to the Blanford and Oates’ edition of 
this work, in the former case the type-locality being given in 
brackets after the reference.. The saving of space thus obtained 
and the use of briefer descriptions has given additional room for 
