122 EFFECTS OF USE AND DISUSE. 



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 

 condition. In the Ateuchus or sacred beetle of the Egyp- 

 tians, 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 opera- 

 tions, 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 dis- 

 use ; for, as many dung-feeding beetles are generally found 

 with their tarsi lost, this must happen early in life ; there- 

 fore 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. Mr. 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 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, else- 

 where 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 oftenest have been 

 blown to sea, and thus destroyed. 



