Cha*. v.] EFFECTS OF USE AND DISUSE. 169 



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 proportion 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 re- 

 quire the use of their wings, are here almost entirely 

 absent; — these several considerations make me believe 

 that the wingless condition of so many Madeira beetles 

 is mainly due to the action of natural selection, com- 

 bined probably with disuse. For during many suc- 

 cessive generations each individual beetle which flew 

 least, either from its wings having been ever so little 

 less perfectly developed or from indolent habit, will 

 have had the best chance of surviving from not being 

 blown out to sea; and, on the other hand, those beetles 

 which most readily took to flight would oftenest have 

 been blown to sea, and thus destroyed. 



The insects in Madeira which are not ground-feed- 

 ers, and which, as certain flower-feeding coleoptera and 

 lepidoptera, must habitually use their wings to gain 

 their subsistence, have, as Mr. Wollaston suspects, their 

 wings not at all reduced, but even enlarged. This is 



