MA CROLEPIDOPTERA 



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related pair, inhabiting the same localities in Oahu and Kauai. It seems to me 

 that possibly the comparative slackness of competition in the Hawaiian Islands may 

 account for this coexistence of two or three similar related forms, of which under 

 severer conditions one would probably have been improved up to the point of com- 

 pletely ousting the others, or perhaps the weaker would have been superseded by 

 a species of a different group. 



Characteristics of the Fauna. 



{a) Absence of primitive forms. 



There are no genera of very early type, such as would help to fill up gaps 

 between previously known forms. The conditions might probably have been favour- 

 able for the preservation of such genera, if they had ever reached the islands, but they 

 do not seem to have reached them. The genera of the first two periods designated 

 above are early rather than late ; they belong to the earlier half of the Lepidoptera, 

 but that is all that can be said for them. Perhaps the islands, old as they must 

 be geologically, are still not old enough for this. 



(3) Prevalent close relationship of species. 



In those genera where the species are numerous, they are also generally very 

 difficult to understand. Had the specimens been without locality-labels, I do not think 

 it would have been possible to have separated the species satisfactorily ; but when 

 arranged in geographical series, the differences, if any, became apparent. This state 

 of things would seem to imply that the elimination of species has not been carried so 

 far as in other regions where there is a sharper competition, which would have tended 

 to increase the divergence, whilst at the same time destroying the intermediates. The 

 climax of difficulty is reached in Scotoryt/ii-a, where many of the species are also very 

 variable, whilst the sexes often differ considerably and are hard to match, and the 

 secondary sexual characters, which often afford a good distinction in the males, are not 

 available in the females. It is of course essential that the sexes of these species should 

 be able to recognise one another with ease, and the visible differences which exist are 

 sometimes so slight or so little obvious that it hardly seems credible that they can be 

 appreciated by the insects themselves ; in such cases it would appear necessary to 

 suppose that the sense of smell has to supply the deficiency. The expansible hair tufts 

 on the genital organs of almost all Lepidoptera are probably scent-producing structures 

 connected with this purpose. On the other hand, if the insects themselves do not 



