The Oologists' Record, June \, 1923. 31 



This is practically the same as many naturalists in this country, 

 including myself, have often stated, but my own definition has 

 always been with the additional controlling factor that before 

 any such variation is entitled to a trinomial it must either first 

 prove to be constant within some given area, or the circumstantial 

 evidence must suffice to form a prima facie reason for its probable 

 distinctness from its nearest allies. Theoretically no bird should 

 be given a trinomial until a series is available for examination 

 but, practically, when a single specimen of a species is obtained 

 at some very great distance from the type locality, showing very 

 obvious variation, a name may, in rare instances, be given pending 

 further investigation. 



The question as to what degree of differentiation constitutes a 

 species or sub-species is one impossible to determine, for variation 

 which in one bird is specific may, in another, not even suffice to give 

 it the status of a sub-species. Thus, difference in size may be a 

 specific character in one bird, sub-specific in a second, and merely 

 individual in a third. For instance, in the Crows, Cuckoos, Shrikes 

 and many other birds, we have in India and Burma a general 

 reduction in the size of the individuals of a species from North 

 to South ; but within this area we have smaller areas in which the 

 size varies but slightly and we are thus able to lay down fairl}^ 

 definite lines of demarkation even when the diminution in measure- 

 ments is not accompanied, as it often is, with other characters. 

 On the other hand, we have birds such as Garrulax pectoralis and 

 Garrulax monileger which differ principally merely in size, yet which 

 inhabit practically the same range. Moreover, throughout their 

 very wide habitat, both species form numerous geographical races 

 which differ from the typical forms in much the same manner 

 and to the same extent. 



The great difficulty, according to some naturalists, in defining 

 sub-species, lies in the differentiation of island forms, which they 

 allege cannot be said to grade into one another. As a matter of 

 fact, however, if series of a species are collected from the two or 

 more islands which form its liabitat, almost invariably certain 

 individuals will be found in each series showing a tendency towards 

 the difference in the size, colour or other variation which foims 

 the feature distinguishing each from its nearest neighbour or 

 neighbours. But the question of trinomialism at once opens up a 

 vast number of other points and, above all others, that of the 



