LAWS OF VARIATION 111 



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 in- 

 herited 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; 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) inhabit- 

 ing 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 numer- 

 ous, which absolutely require the use of their wings, are here al- 

 most entirely absent. These several considerations make me be- 

 lieve 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 individ- 

 ual 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-feeders, and which, 

 as certain flower-feeding coleoptera and lepidoptera, must habit- 

 ually use their wings to gain their subsistence, have, as Mr. Wol- 

 laston 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 suc- 

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



