CHAP. V.] EFFECTS OF USE AND DISUSE. 101 



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 specimens 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 condition. In the Ateuchus or sacred beetle of 

 the Egyptians, they are totally deficient. The evidence that acci- 

 dental mutilations 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 modifications 

 of structure which are wholly, or mainly, due to natural selection. 

 Mr. Wollaston has discovered the remarkable fact that 200 beetles, 

 out of the 550 species (but more are now known) inhabiting Madeira, 

 are so far deficient in wings that they cannot fly ; and that, of the 

 twenty-nine endemic genera, no less than twenty-three have all 

 their species in this condition ! Several facts, namely, that beetles 

 in many parts of the world are frequently blown to sea and perish ; 

 that the beetles in Madeira, as observed by Mr. Wollaston, lie much 

 concealed, until the wind lulls and the sun shines ; that the pro- 

 portion of wingless beetles is larger on the exposed Desertas than 

 in Madeira itself ; and especially the extraordinary fact, so strongly 

 insisted on by Mr. Wollaston, that certain large groups of beetles, 

 elsewhere excessively numerous, which absolutely require the use 

 of their wings, are here almost entirely absent ; these several con- 

 siderations make me believe that the wingless condition of so 

 many Madeira beetles is mainly due to the action of natural selec- 

 tion, combined probably with disuse. For during many successive 

 generations each individual beetle which flew least, either from its 

 wings having been ever so little less oerfectlv developed or front 



