W. H. NUKNEY ON SCALE EVOLUTION. 103 



The foregoing comparisons lead ns to the conclusion that 

 numerous transitional forms of scale are very rare, such a phenome- 

 non as occurs in Ithomia being unique in its own group. The 

 question naturally arises, how is it that Ithomia3 alone show scale 

 evolution more perfectly than do other insects? On the supposition 

 that Ithomia is an extremely ancient type, if not indeed a truly 

 primitive form, this may be satisfactorily answered. Palasonto- 

 logical evidence, however, by no means bears this out. The earliest 

 occurrences of Lepidoptera in geological strata, excluding the 

 disputed Palceontina oolitica, are of a very different group, the hawk 

 moths or Sphingidae, and in no way allied to Ithomia?, although 

 such evidence is from the imperfection of the record not at all 

 conclusive. On structural evidence the primitive position may 

 probably be assigned to the Swift moths or Hepialidre. It is 

 then all the more singular that with such comparatively high 

 development in other respects, so many and curious transitional 

 forms of hair and scale should occur in Ithomia and its allies, and 

 it is worthy of passing note that the true battledor scale so charac- 

 teristic of the butterfly known as the Azure blue does not occur 

 in the Ithomian series. Perhaps we are altogether mistaken in 

 assigning so high a development to the battledor scale. This 

 negative view T is apparently borne out by a reference to some of the 

 lower scaled insects. Certain white-ants (admittedly a very 

 ancient group), found only in a fossil state, are furnished, not as 

 might be expected with coverings of the hair scale type or simple 

 hair, but are clothed with near approaches to the battledor type. 

 In Perientomum I believe this is markedly the case. Amongst the 

 Poduraa, or springtails, the body covering is almost without excep- 

 tion composed of scales of the crenate battledor type possessing a 

 high, possibly the highest development, notwithstanding that the 

 creatures themselves are of the most lowly degree, on this account 

 having been shelved from the insect series, and, indeed, considered 

 as insect prototypes. The question of the evolution of true scales 

 from simple hairs is thus thrown back immeasurably further into 

 the past. That this battledor type is really a development and not 

 a primitive form must, I think, be allowed when it is considered 

 that beetles, which are undoubtedly of a higher type than even 

 butterflies (Agassiz notwithstanding) possess hardly any other 

 description of scale. By the facts relating to the Poduras the 

 reverse is of course implied. There are great difficulties in either 



