162 Mr. Robert M'Lachlan on Acentropus. 



an instance of differences sufficient to be considered 

 specific in the anal apparatus, without corresponding' 

 general discrepancies, though these latter are often diffi- 

 cult to explain in words. Local variation sometimes 

 exists in the same species, and so does individual varia- 

 tion, and occasionally to an extent, in large insects, that 

 would throw the small differences exhibited in the 

 appendages of the Acentropi into the shade ; but, never- 

 theless, the fact remains unassailable, that the most 

 important organs, those upon which the perpetuation of 

 the species depends, are those in which, as a rule, the 

 best characters are found : and this latter remark obtains 

 equally with regard to sexual appendages not immedi- 

 ately connected with the genital apparatus, for, in insects, 

 domestication has not had an opportunity of forcing 

 these peculiarities into abnormal development, nor, by 

 altering the conditions of existence, of rendering them 

 useless, and consequently aborted. In almost all orders 

 of insects, sexual characters have been applied to specific 

 separation with the best and sm'est results. Lepidopterists 

 (with few exceptions) continue to allow the eye to be 

 attracted by beauty of colour, or variation in design of 

 markings, leaving more subtle characters neglected, either 

 designedly, or because their examination, by rendering 

 necessary the removal of the scales, makes the specimens 

 " imperfect " as they term it. I venture to predict that 

 the day is not far distant when coloured plates of butter- 

 flies, without details of structure, will be valued only 

 as pretty pictures, comparatively useless for scientific 

 purposes. 



Explanation of the figures on p. 159. 



Fig. 1, Lateral view of appendages of a male from Hampstead; a, ap- 

 pendices inferiores ; b, boat-shaped lobe ; c, superior process ; 

 d, penis ; * e, apex of penis from beneath, more enlarged. 



2. Example from Burton-on-Trent. 



3. „ „ A. niveus (Staiidinger). 



4. „ „ A. latipennis (Staudinger). 



• The teeth are somewhat exaggerated in all the figures. 



