THE INHERITANCE OF MELANISM IN THE 

 GENUS TEPHROSIA(ECTROFIS)WlTll SOME 

 CONSIDERATION OF THE INCONSTANCY OF 

 UNIT CHARACTERS UNDER CROSSING. 



By J. W. HESLOP HARRISON, D.Sc. 

 (With 3 Text-figures.)^ 



I. Introductory. 



(1) General. 



"Species are but judgments — judgments of variable value and 

 often very fallible judgments " says Asa Gray, and certainly no genus 

 would seem to bear more eloquent testimony to the apparent truth of 

 the dictum than Tephrosia. Generation after generation of entomolo- 

 gists have used certain of its members as a kind of battleground upon 

 which to conduct their wordy warfare as to what constitutes a species. 

 However, it must be assumed that all of its members have formed such 

 acute subjects for controversy; everyone, no matter whether his ten- 

 dencies were to "lump" or to "split," has ever ventured to refuse specific 

 rank to Tephrosia luridata {extersaria) and T. consonaria, for their 

 position is unassailable. Far different' is it with Tephrosia crepuscu- 

 laria and T. bistortata. Some have maintained that the two represented, 

 at best, races of the same species, whilst others have just as stoutly 

 insisted that they were specifically distinct. And strangely enough, 

 although the holders of identical views did not necessarily agree 

 amongst themselves in the reasons for the faith that was in them, 

 each of the contending factions could only see its side of the shield, and 

 so the battle continued. Neither side would give way, and therefore on 

 every occasion that the question was raised it ended with matters practi- 

 cally in their original position. 



To me the whole matter seems to hinge on the validity of Gray's 

 definition of a species. Most of the disputants, although probably not 

 aware that Gray had ever used the phrase, argued as if it were perfectly 



^ The same applies to certain American species of the Tephrosia bistortata group. 



