16 ENTOMOLOGICAL SOCIETY 



in some respects unique, they are not more wonderful nor more 

 difficult of explanation than numerous other differences to be 

 found among the members of this class. Such extreme cases 

 are, however, of special interest, since they illustrate more strik 

 ingly the evolutionary status of the group. Among the highly 

 adaptive insects it would be extremely rash 10 deny that any or 

 all structural characters would find an explanation based on 

 natural selection,* and in the Diplopoda we have also many pecu 

 liarities of apparent utility which obviously may have been brought 

 to their present perfection in this way. It is, nevertheless, worthy 

 of note that in the Diplopoda such adaptations are almost ex 

 clusively sexual, in accordance with the extremely simple ecologic 

 relationships noted above. 



The Diplopoda have probably not been threatened with ex 

 tinction by natural enemies, nor are their numbers kept down by 

 inadequate food supplies. With them the struggle for existence 

 centers rather about the problem of reproduction, their methods 

 being at once primitive and complicated. In the different orders 

 and families the extremely varied copulatory legs have been sup 

 plemented by other contrivances frequently similar in function 

 and yet different in structure and origin. Specially thickened, or 

 in other cases unusually elongated, claws, pads of hairs, fleshv 

 soles or cushions, rows of tubercles and other contrivances, have, 

 for example, been variously and independently provided to render 

 the last joint of the legs of males more effective in assisting copula 

 tion. The mechanical ingenuity of the group, so to speak, 

 seems to have exhausted itself in this direction, and yet structure 

 and color, although neglected by selection, have by no means re 

 mained uniform. 



Even in dealing with groups more adaptive than the Diplo 

 poda, writers on natural and other forms of selection have been 



* Professor Romanes held that a majority of minor specific differences 

 have no assignable utility, a view which he supported by reference to the 

 color differences of birds and mammals. Had his observations extended 

 to the Diplopoda there would have been no need of such limitations either 

 to shades of color or to specific characters, since in this group structural 

 characters of genera and families are as obviously useless from the stand 

 point of relation to environment It is true, as pointed out by Professor 

 Romanes, that the birds and mammals " represent the highest products 

 of evolution in respect of organization," that is, they have been sub 

 jected to an extended experience of acute natural selection throughout 

 which there would have been a strong tendency against the accentuation 

 of certain classes of structural characters, though, as in the Diplopoda, 

 divergences might continue to accumulate in internal or reproductive 

 structures which do not affect external appearance, or efficiency in the 

 struggle for existence. 



