296 Dr. H. Eltringham on Certain Forms of Acraea. 



and constant differences between the two forms are dif- 

 ferences of pattern. The structural differences are very 

 slight and open to question. In my monograph of the 

 genus I stated that " with our present conception of the 

 evolutionary nature of species formation the precise limita- 

 tion of what is called a ' species ' has necessarily lost much 

 of its importance, as compared with the recognition of the 

 degrees of affinity which appear to obtain between the 

 forms studied. ... In many cases it is extremely difficult, 

 if not impossible, to decide whether a form has yet passed 

 over that dividing line which separates one true species 

 from another. The difficulty experienced is merely a con- 

 firmation of our theories of species formation." A. siliana 

 does not appear to occur in precisely the same localities 

 as A. masamba. The characteristics of A. siliana as com- 

 pared with A. masamba are equivalent to those I should 

 regard as applying to a subspecies, i.e. a geographical race 

 not entirely and specifically separate. M. Oberthiir prefers 

 to regard the two forms as distinct species. After all, it 

 is of little real importance which view we adopt. The case 

 is similar to that of A. welwitschii and A. anetnosa. 



Finally, I should wish to express my appreciation of 

 M. Oberthur's most valuable and interesting contribution 

 to our knowledge of the Acraeas, of M. Culot's exquisite 

 plates, and of Professor Houlbert's beautiful drawings. 

 The structural features of the Lepidoptera have too long 

 been obscured by the dazzling beauty of their wings, 

 and we shall look forward with pleasurable anticipation 

 to further valuable communications from so ideal a 

 collaboration as that of M. Charles Oberthiir and Professor 

 Houlbert. 



Explanation op Plate LXXIV. 



Figs. 1-5. Scales from f.-w. apical area of A. masamba. 

 6-10. „ ,, ,, „ ,, A. siliana. 



11-13. „ ,, „ internal angle of A. masamba. 

 14-16. „ ,, ,, ,, ,, A. siliana. 



December 29, 1910. 



