1922.] Species and Suhsperies. 183 



By the phrase "remaining unchanged^' I am not, of 

 course, referring to mere depth of colour-tones produced by 

 chemical processes in the pigment contained in the feathers 

 as the result of external climatic agencies, but to actual 

 differences in colour-pattern. 



But to return once more to the examples of specific 

 vai'iation which we have quoted at the outset of these 

 remarks, and which have appeared to me to be convenient 

 examples of what may be termed mutational subspecies as 

 opposed to environmental, there would undoubtedly seem to 

 be a practical difficulty in the matter of nomenclature in 

 connection with them. For if wo roundly regard them as 

 " species " our nomenclature will fall short of indicating (as 

 trinomials tlo so conveniently) their undoubted genetic rela- 

 tionships to the typical races — Podiceps cristatiis infiiscatus, 

 for instance, being undoubtedly genetically allied to P. c. 

 cristatus. 



My meaning may be rendered clearer by what immediately 

 follows. 



Mr. Bonhote in his letter to ' The Ibis ' on " Subspecies 

 and their part in Evolution '' (Ibis, 1921, p. 721) writes, as 

 follows : — " 1 had always understood that a true subspecies 

 was always supposed to be restricted to the latter cause [i. e. 

 environment], and certainly think it should be so." This 

 may be so or not; certainly it is not followed out in practice 

 by the majority of systematists ; but if it is so, it follows 

 that Mr. Bonhote would either consider that the examples I 

 have quoted owe their origin to environmental causes (an 

 opinion which with his experience of breeding mammals and 

 birds I should hesitate to attribute to him), or that ihcy are 

 not "true subspecies," and that in so writing them down 

 systematists have erred. If this latter conclusion is correct, 

 the question at once arises, ivJiat are they ? The question is 

 a practical one, apart from the more deep-seated one which 

 underlies our recognition that this kind of subspecies diflers 

 from a purely environmental subspecies, such, for example, 

 as a dark form originating in a damp humid climate. 



The only solution wdiich occurs to me at the present 



