SVNGAMY UNDERLIES TRANSITION 69 



kindness of Mr. C. A. Wiggins and Mr. A. H. Harrison, 

 the Hope Department has recently been presented with 

 an exceedingly fine series of butterflies from both east 

 and west of the northern shores of the Victoria Nyanza. 

 These have been carefully studied by Mr. S. A. Neave, 

 M.A., B.Sc., of Magdalen College, Oxford, who finds that 

 the typical niavius occurs in great abundance to the west 

 of the lake, while on the east he meets, in both collections, 

 with varieties beautifully intermediate between it and 

 dominie anus. These varieties, occurring precisely in the 

 zone where the eastern form meets the western, complete 

 for the systematist the transition which renders domini- 

 canus a variety of niavius 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. Nevertheless, if complete enough, the transi- 

 tion of forms on the same area always raises the strong 

 presumption that we are dealing with a syngamic com- 

 munity. 



Probably the most remarkable series of transitional 

 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 'Varia- 

 tion des Heliconia thelxiope et vesta ' (Rennes, February, 

 1902). 



The failure of Diagnosis as the sole test of Species- 



The method of Diagnosis, at its clearest and simplest, 

 is always consistent with, and often strongly suggests, an 

 underlying 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 Epigony as 

 decisive ; and if he has not direct proof of the existence of 

 either of these, indirect evidence is, at any rate provision- 



