Seite - 148 - in The Origin of Species

148 ORIGIN OF SPECIES it is probable that the nearly wingless condition of several birds, now inhabiting or which lately inhabited several oceanic islands, tenanted by no beasts of prey, has been caused by disuse. The ostrich indeed inhabits continents, and is exposed to danger from which it cannot escape by flight, but it can defend itself by kicking its enemies, as efficiently as many quadrupeds. We may believe that the progenitor of the ostrich genus had habits like those of the bustard, and that, as the size and weight of its body were increased during successive generations, its legs were used more, and its wings less, until they became incapable of flight. Kirby has remarked (and I have observed the same fact) that the anterior tarsi, or feet, of many male dung-feeding beetles are often broken off; he examined seventeen speci- mens in his own collection, and not one had even a relic left. In the Onites apelles the tarsi are so habitually lost, that the insect has been described as not having them. In some other genera they are present, but in a rudimentary condi- tion. In the Ateuchus or sacred beetle of the Egyptians, they are totally deficient. The evidence that accidental mu- tilations can be inherited is at present not decisive ; but the remarkable cases observed by Brown-Sequard in guinea- pigs, of the inherited effects of operations, should make us cautious in denying this tendency. Hence it will perhaps be safest to look at the entire absence of the anterior tarsi in Ateuchus, and their rudimentary condition in some other genera, not as cases of inherited mutilations, but as due to the effects of long-continued disuse; for as many dung- feeding beetles are generally found with their tarsi lost, this must happen early in life; therefore the tarsi cannot be of much importance or be much used by these insects. In some cases we might easily put down to disuse modifi- cations of structure which are wholly, or mainly, due to natural selection. Air. Wollaston has discovered the remark- able fact that 200 beetles, out of the 550 species (but more are now known) inhabiting Madeira, are so far defi.cient in wings that they cannot fly; and that, of the twenty-nine endemic genera, no less than twenty-three have all their spe- cies in this condition ! Several facts,—namely, that beetles