rOI.OKA'l'lON AFKECTKD BY 'I'llK EXVIRONUI KKT. 57 



tlimslies and otbov snail-eatiug birds on the Lower Rhine than 

 at Bonn, or rice rrrsa if tlie " citron veHow *" variety is the 

 more eouspicnoiis. 



The suffusion of the markings and the duller colour which is 

 said to oi'.eur among Aljiine butterflies is in strilving contrast 

 with the unusual brilliancy of colour which is noticeable in 

 Alpine plants. 



The latter change is said to be owing te> the less numbers of 

 insects whiclu'ross-fertilise the flowers; and hence the need for 

 a greater effort, so to speak, on the part of the plant to attract 

 them and thus seenre the desirable effects of their visitations. 



This might be urged as an objection to the climatic 

 influence, on the gnmnds of unlike effects in the two cases. 

 But it is perhaps hardly niH'cssary to point out that the 

 pigments of the butterflies' wings are different from those of 

 the flowers, and that the }>hysiological ju-ocesses which take 

 [dace in the bodies of animals without chlorophyll are in thi' 

 flrst place different from those of chlorophyll-bearing plants. 

 And in the second place the same t'onditions may produce 

 difl'erent effects. 



Examples of Melanic Varieties fo\md upon Islands. 



There are a good many other examjiles of a tendency towards 

 melanism — more or less realised— among the inhabitants of 

 islands. 



The Galapagos Islands consist of a group of islands, of 

 various areas, situated some live hundred miles to the west 

 of the South American continent. One of the most charac- 

 teristic inhabitants of these islands is the curious marine 

 Iguanoid lizard, Oirocephahis. It is thus described by 

 Dai'win : " It is a hideous-looking creature, of a dirty black 

 colour, stupid and sluggish in its movements. The usual 



