( xciv ) 



was at systematic work I know I longed to have no other 

 difficulty (great enough) than deciding whether the form was 

 distinct enougli to deserve a name, and not to be haunted with 

 undefined and unanswerable questions whether it was a true 

 species. What a jump it is from a well-marked variety, pro- 

 duced by natural cause, to a species pi-oduced by the separate 

 act of the hand of God ! But I am running on foolishly. 

 By the way, I met the other day Phillips, the palaeontologist, 

 and he asked me, ' How do you define a species 1 ' I answered, 

 * I cannot.' Whereupon he said, ' At last I have found out 

 the only true definition — any form which has ever had a 

 specific name ! ' " * 



The idea of a species as an inter-breeding community, as 

 syngamic, is, I ])elieve, the more or less acknowledged found- 

 ation of the importance given to transition. This will become 

 clearer from the consideration of a concrete example. The 

 common l)lack-and-white Danaine butterfly, Amaiiris niavius 

 of West Africa, is represented on the East and South-East 

 Coasts by a very similar butterfly, distinguished by the greater 

 size of the largest white patch, and of the white spot in the 

 cell of the fore-wing. Both forms are very constant in the 

 areas over which they were known, and on these constant 

 easily recognisable characters the eastern butterfly was 

 described as a distinct species under the name of A. domini- 

 canus. Aurivillius, however, in his valuable Catalogue refuses 

 to recognise this latter as a distinct species, and considers it 

 as the dominicanus variety of niavms. Through the kind- 

 ness 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 Lake Victoria Nyanza. These have been 

 carefully studied by Mr. S. A. Neave, B.A., of Magdalen 

 College, Oxford, who finds that the typical niavms occurs in 

 great abundance to the west of the lake, while on the east he 

 meets, in both collections, with varieties beautifully inter- 

 mediate between it and dominicanus. These varieties, 

 occurring precisely in the zone where the eastern foi-m meets 

 the western, complete for the systematist the transition which 



* " More Letters," vol. i, p. 127, Letter 79. 



