MELANIC VARIATION IN LEPIDOPTERA. I35 



The manner of increasing that advantage in proportion to 

 the excess of energy resulting from its possession has been 

 indicated, and if not actually proved, has I think been fairly 

 argued from analogy, by comparison with the chemical action 

 known to occur in plants. 



It has been shown how the same kind of action might not 

 unreasonably account for similar results in birds, animals, and 

 human beings, contributing in each instance to the advantage 

 of the subject ; and if the sketch has been somewhat imperfect, 

 I rejoice to feel that there is no scarcity of naturalists more 

 able than myself who will gladly apply themselves to the task, 

 either of effacing it entirely, or of filling in the required details. 



The proved existence of what are merely extreme local 

 varieties of known and described species should warn us that 

 while on the one hand we should avoid a too hasty conclusion 

 that specimens exhibiting some affinities of colour and struc- 

 ture yet found to differ in a more or less important degree, are 

 not specifically distinct from others with which we are ac- 

 quainted, we should even more carefully guard ourselves against 

 giving separate names to such divergent forms as if they were 

 true species, simply because they come to us from some re- 

 mote locality, or because we possess no series of connecting 

 links between these and their nearest allies. 



I am by no means disposed entirely to condemn the system 

 of trinomial nomenclature now widely adopted in America, 

 especially in ornithology; provided always that this system is con- 

 fined to climatic or geographical races, varying according to known 

 conditions, such as latitude, elevation, temperature, moisture, 

 etc. It might perhaps, as in the case of many of the Shetland 

 insects, simplify rather than confuse the process of exact recog- 

 nition. The abuse rather than the use of the system is to be 

 feared. Should everyone who discovers a slight varietal differ- 

 ence think himself entitled to apply to it a third name, the 



