235 



able salt and brackish lakes being the primary cause of its 

 retrograclation.i 



Owing to the light membranous body of insects, they Avere 

 less likely to be destroyed^ in pre-historic evolutions than were 

 vertebrates and many invertebrates ; consequently future re- 

 searches in the rich deposits of the Rocky Mountain tertiaries 

 may yet reveal the fossil ancestor of Amblychila. 



As a secondary adaptation, I mention the pubescence of the 

 middle tibia in the male of Megacephalini and Cicindela (ex- 

 cepting in Q. pilatei and C. maga, where it is glabrous). It is 

 intended for a firmer hold of the female during copulation ; in 

 Amblychila the dilation of the anterior tarsi in the male was 

 dropped as useless, probably owing to the smooth cylindrical 

 thorax of the female, and was replaced by an acute hind 

 trochanter^ for firmer insertion into the funnel-shaped pores 

 between the ridges of the elytra of tlie female. This structure 

 was useless to the female and therefore the troclianter re- 

 mained blunt. We find similar inherited adaptations in the 

 serrulate and curved middle tibia of Galosoma sayi ;^ the dilation 

 of the anterior tarsi was in this instance preserved. Although 

 O. sayi occurs frequently in Kansas and thereabouts, its fre- 

 quency is probably checked by some enemy ; its large size, and 

 perhaps other causes, lessen its number. The interrupted 

 elevations between the longitudinal ridges of its elytra are also, 

 perhaps, fit for the acute trochanter of the male. 



Whenever we find characters dropped because they are of 

 no apparent use, we find them existing elsewhere, where they 

 are probably also useless. They are merely — as are, for in- 

 stance, the arthropodous trochanters — rudimentary organs 

 which become important indications in comparative anatomy 

 for tracing their ancestral connections, at the same time teach- 



1 LeConte : Classification of the coleoptera of North America, p. 1. 



2 LeConte: Address {I. c), p. 8. " Cataclysms and submergences, which would 

 annihilate the higher animals, would only float the temporarily asphyxiated insect, or 

 the tree trunks containing the larvae and pupae to other neighboring lands." 



3 Horn: Sexual characters of North American Cicindelidae . . . (Trans. Amer. 

 Entora. Soc, 1875, v. 5, p. 232-240, pi. 1 in part) (Misc. papers on Amer. coleoptera, 

 p. 232-240, pi. 1 in part), pi. 1, fig. 18. 



^ Horn: ibid., pi. 1, fig. 26. 



