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that it was a case of many keys to open one lock ; but after 

 an extensive study, along with Dr. David Sharp, of these 

 organs in Coleoptra, and their function during copulation, I 

 was forced to change my opinion, for the evidence shows that 

 in many cases the key fits its lock, and its own lock only. 

 In these cases the coadaptation is between the meml)ranous 

 internal sac and its armature and the membranous uterus. 

 In the Derbidae I have observed a coadaptation between the 

 genital styles and anal segment and certain knobs and de- 

 pressions on the female, a coadaptation I did not suspect until 

 I observed the sexes in copula. How far some of the minor 

 changes (i. e. N. koae, N. Jcoae-phyUodii and oaJiuensis) would 

 prevent fertilization it is impossible to say at present, but that 

 such structures as the aedeagi of N. lioae, N. perl-insi. X. 

 raillardiae, N. ipomoeicola, N. lialia, N. sharpi and T. f/if- 

 fardi could all perform the same luechanical operation in a 

 similar manner is highly improbable. On the other hand, 

 to account for these structures along with a coadaptation in 

 the female by ISTatural Selection is to me unthinkable ; the 

 more one tries to follow out in thought sucli an operation the 

 greater the difficulty becomes. 



Isolation. Our collections are not complete enough for us 

 to judge of the full effect of isolation on species formation, 

 but enough is known to demonstrate that isolation and species 

 formation coincide to a very large extent. A few species are 

 dispersed over two or more islands, others over one island, 

 but a large number have very limited habitats. D. mimhUis 

 is a good example of this limited range, it being found only 

 on a small ridge a few feet wide and not more than a quarter 

 of a mile long.* According to our present collections Oahu 

 has 42 species, Hawaii 20, Kauai 12, Maui 11, Molokai 7 

 and Lanai 5. This does not represent the richness of, but 

 only the amount of collecting done in each island. 



In spite of this it is possible that a study of the distriliu- 

 tion of these insects in the Archipelago may lead to some in- 

 teresting results, if it be borne in mind that more extensive 

 collecting is likely to modify the present conclusions. That 

 more species will be found in the Island of Hawaii, when the 



*Mr. Timberlake has since found it on the Lanihuli ridge, on the 

 western side of Nuiianu Valley, and Mount Kaala of the Waianae 

 Range. — Ed. 



