( xcv ) 



I'enders dominicanus a variety of niavms and not a distinct 

 species. But it is clear that they do more than this ; they 

 make it almost certain that the two forms freely interbreed, 

 and constitute but a single syngamic community. 



This is one of the remarkably clear examples. In many 

 cases we know the transition, but the extremes are not sorted 

 out in different parts of the total area of distribution. Never- 

 theless if complete enough the transition of forms on the 

 same area always raises the strong presumption that we are 

 dealing with a syngamic community. 



Probably the most remarkable series of ti'ansitional varieties 

 ever depicted is that shown in the eleven quarto plates of 

 the last part of Monsieur Charles Oberthiir's great " Etudes 

 d'Entomologie," entitled " Variation des Helicoma ilielxioiie et 

 vesta^' (Rennes, February, 1902). 



The method of diagnosis, at its clearest and simplest, is 

 always consistent with, and often strongly suggests, an vicder- 

 lying syngamy. There are, however, numberless examples 

 belonging to various categories in which a rigid adherence 

 to diagnosis cannot avail. In these cases the systematist 

 frankly appeals to syngamy or synepigony as decisive ; and 

 if he has not direct proof of the existence of either of these, 

 indirect evidence is, at any rate provisionally, regarded as 

 sufficient. 



I, Dimorjihisvi, Polymorphism : — In an ever-increasing 

 number of examples an assemblage of individuals is regarded 

 as a single species, although split up into two or more widely 

 different and sharply separated groups, between which transi- 

 tional varieties are excessively rare or even unknown. For 

 instance, the extremely abundant, widely distributed butterfly 

 Liinnas chrysip'pus includes among other forms one in which 

 the black-and-white tip is wanting from the fore-wing, the 

 doripims ( = khtgii) form. This variety is sharply cut off from 

 the type fcrm. Although faint traces of a former white bar 

 can be made out in doripjms, I have never seen, among 

 thousands of individuals, the material out of which a good 

 transitional series between it and c/tri/sipjms could be con- 

 structed. In this case the evidence of syngamy is strong and 

 complete ; for Col. Yerbury has recorded the fact that the 



