Chap. V.] EFFECTS OF USE AND DISUSE. IOC 



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 proportion of wingless beetles is largei on the 

 exposed Desertas than in Madeira itself; and especially the extra- 

 ordinary 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 considerations make me believe that the 

 wingless condition of so many Madeira beetles is mainly due to 

 the action of natural selection, 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 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 oltenest have 

 been blown to sea, and thus destroyed. 



The insects in Madeira which are not ground-feeders, 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 

 quite compatible with the action of natural selection. For when a 

 new insect first arrived on the island, the tendency of natural 

 selection to enlarge or to reduce the wings, would depend on 

 whether a greater number of individuals were saved by successfully 

 battling with the winds, or by giving up the attempt and rarely or 

 never flying. As with mariners shipwrecked near a coast, it would 

 have been better for the good swimmers if they had been able tc 

 swim still further, whereas it would have been better for the bad 



