294 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



(see fig. 76) on the legs of a fresh-water crab in Chili, occurs 

 identical in species in the Philippines and in Java, but on per- 

 fectly different crabs. It would be easy to multiply instances, 

 but these will suffice, I believe, to show that any attempt to 

 explain them by the action of constant marine currents must 

 altogether fail. Other causes must here have combined to 

 produce so striking a resemblance between the faunas of 

 islands lying so far apart ; but it would be difficult to discover 

 them in every case. Wallace has justly observed in his great 

 work that such cases ought, under the circumstances, to be 

 regarded as a proof of the justice of the hypothesis that those 

 types which have occasioned the similarity of remote faunas 

 must have had a very long historical duration, persisting very 

 likely throughout many geological epochs. Also it must not 

 be forgotten that the convergence or parallelism of different 

 species may sometimes have led to the formation of two simi- 

 lar faunas in very remote places in nodern times. This, 

 however, is not the proper place for a discussion of this inter- 

 esting point, and I must refer the reader who is particularly 

 interested in it to the brief remarks he will find in the 

 Appendix. 114 



(b) The wind as a means of dispersal. It is evident that 

 the distribution of all flying creatures, i.e. the selection of forms 

 among them, must in a great degree depend on the direction 

 and strength of atmospheric currents, whether these be regular 

 winds or irregular storms ; but it is a matter of very great 

 difficulty to determine what share each mode of atmospheric 

 motion may have, or how they may co-operate. 



Instances of animals being carried by wind-storms far 

 beyond the limits of their native province, or even beyond seas, 

 are universally known, and it must here suffice to refer the 

 reader to the chapter on the Means of Dispersal in Darwin's 

 work, in which a great number of independent examples are 

 given. Still we are justified in inquiring whether indeed such 

 an accidental transportation of solitary individuals to countries 

 where they are merely interlopers, can have often led to the 

 acclimatisation of a species in a new country. For it must 

 not be forgotten that, independently of the difficulty they will 



