( XV ) 



which it would be possible to draw a definite line; but in 

 many cases the delimitation of frontier must be arbitrarj'. 

 The President had brought forward a striking instance in the 

 case of Amauris niavius and A. dominicanus, which had been 

 shown by Mr. ISTeave to be connected in the Uganda district 

 by a complete series of intermediate forms. Still more strik- 

 ing perhaps was the case of Mylothris chloris and 31. agathina, 

 which had always been considered as completely distinct as 

 any two species in the genus, but which intergraded with one 

 another in the same district of Uganda. In the genus Colias 

 again, the speaker, after a careful study of Mr. Elwes' well- 

 known papers, found himself in complete agreement with the 

 opinions there expressed as to the impossibility of separating 

 various forms that had received distinct specific names. 

 " Typical " forms, for instance, of C. palmio and G. chrysotheme 

 in the Old "World, and of C. philodice and C. euryfheme in the 

 New, were sufiiciently dissimilar ; yet in certain parts of their 

 area of distribiition, these forms seemed to be inextricably 

 interconnected. 



It appeared to be now admitted by many naturalists that 

 the question, " What is a species 1 " resolved itself into a 

 matter of general convenience. What then, fi^om this point 

 of view, were the best criteria of specific distinctness ? The 

 President in his recent Address had suggested more than one 

 such test. Of these the most crucial was probably epigony. 

 It met such cases as those of seasonal dimorphism, where the 

 syngamic test was inapplicable ; moreover it had the advant- 

 age of getting rid altogether of the arbitrary element. 

 Evidence as to sjngamy was extremely valuable, and in most 

 cases was more easily obtained ; but it could hardly be said 

 that syngamy used as a test of specific distinction was able 

 to dispense with the personal equation. Syngamy was con- 

 trolled by sexual prefei-ence ; of this many degrees were 

 known to exist. On the one hand there was perfectly free 

 interbreeding, on the other the " rai-e and occasional inter- 

 breeding" Avhich, as Prof. Poulton said, "is not syngamy." 

 Somewhere among the intermediate stages the line must be 

 drawn, and when drawn it would still be arbitrary. 



On the question of sterility of first crosses and of hybrids, 



