of the Ratufa (Sciurus) bicolor Oroup. 491 



characteristics and assume those of the race into whose terri- 

 tory they had been imported *. 



What, then, should we do ? Are we to ignore these 

 differences altogether? That could hardly be done without 

 acknowledging our incompetence as systematists, besides 

 which it should be borne in mind that many of these forms 

 are in reality incipient species, and, in time to come, to have 

 them all carefully described and enumerated will surely 

 throw considerable light on the causes affecting variation, the 

 period required to fix a variety, and questions such as these, 

 about which at present we know hardly the rudimental facts, 

 owing to our absolute lack of reliable descriptions and data of 

 specimens collected so recently as fifty or sixty years ago. 



It seems to me therefore that such forms should be noticed 

 wherever they occur, and the chief question is, in what 

 manner should they be designated ? This at once leads us 

 to the vexed question of trinomials, which subject I have 

 neither the ability or knowledge to dilate upon : personally 

 I use trinomials, as being the shortest, simplest, and most 

 concise way of dealing with varieties due to geographical or 

 climatic causes ; it is used with great success by Americans, 

 who in the study and classification of mammals are certainly 

 ahead of the naturalists of most countries. 



As Mr. Blanford remarks in his paper on Sciurus indicusf, 

 trinomials are doubtless used for variations induced by many 

 other causes ; but one reason I would venture to put forward 

 for the restriction of trinomials to geograpliical or climatic 

 races is that when these forms become sufficiently differen- 

 tiated to be regarded as true species no change of nomen- 

 clature need be made. 



The evolution of the species must of necessity be a slow 

 process, and a stage of evolution must sooner or later be 

 reached in which the characteristics which would entitle it 

 to specific rank will become very precarious and opinions will 

 differ as to its correct designation, some authorities calling it 

 a variety of a well-known species, while others will give it a 

 specific name, and confusion is bound to result. Admit tri- 

 nomials, and he who considers it a species will simply omit the 



* This has been proved by experiment (chiefly with regard to hot and 

 cold forms) with insects, and possibly similar results, though hardly as 

 striking, could be arrived at with squirrels ; the subject is one which it 

 would be impossible to demonstrate by actual experiment — it might take 

 two generations or it might take thirty. One is, however, justified in 

 judging by analogy. 



f Journ. Bombay N. H. Soc. vol. xi. p. 300. 



