PASSERINE BIEDS OF CEYLON. 23 



gradually realized that this classification was hardly sufficient 

 in the case of many widely distributed species. It was 

 apparent, for example, that with many birds which ranged all 

 over the Indian Empire forms from the deserts of North-West 

 India differed noticeably and constantly, on the one hand, 

 from the forms met with in the Himalayas, and, on the other 

 hand, from those found in Ceylon or Southern Burma, though 

 each geographical race passed into the next by the most 

 gradual transitions throughout the intervening areas. Under 

 the old binomial system all these geographical races had either 

 to be lumped together under one specific name, or split into a 

 variety of species with very minor distinctions. Sometimes 

 one course was adopted, sometimes the other. In Gates' and 

 Blanford's " Birds of British India " the geographical races 

 of the Madras Red-vented Bulbul, which is found practically 

 all over India and Burma, are divided into six different species. 

 On the other hand, the common Indian Crow Pheasant, in 

 which there are several well-marked geographical races, is 

 treated as one species. 



To meet the situation, modern ornithologists, wherever 

 necessary, have adopted a trinomial classification, which 

 enables them to differentiate sub-species. For the definition 

 of a sub-species I quote Mr. Stuart Baker: " A sub-species is 

 a geographical race or variation differing in some respect 

 from the form first described as the species, yet linked to it 

 by other intermediate forms found in intervening areas. 

 It is essential, however, that to entitle such a variation to a 

 trinomial, it should have arrived at a point in its evolution 

 sufficiently advanced to enable it to exist as a permanent form 

 within some definite area. From this it will be seen that a 

 sub-species is merely a term for a species in the making."* 



The principle on which the system is worked may be 

 exx^lained briefly as follows : Where it is necessary to divide 

 a species, the sub-species identical with the form from which 

 the species was originally described is expressed by repeating 

 the specific name ; the new sub-species is given an appropriate 



* " Sub-species and the field Naturalist." Journal of the Bombay 

 Natural History Society. May, 1919, Vol. XXVI., part 2, p. 518. 



