131 [Vol. XXXV. 



lu tlie far north of the Arctic Regions the creatures 

 turn white in winter, while in summer their plumage and 

 pelage are mottled or variegated to match the various 

 shades o£ heather and lichens which are characteristic of 

 the moors and tundras. 



Amongst those birds whose plumage is coloured for pro- 

 tection the Goatsuckers stand out pre-eminently. We find 

 that those Goatsuckers inhabiting more fertile regions have 

 dark plumage of various shades of brown, grey, and buff to 

 match the scrub they live in, while those of the desert have 

 sand-coloured plumage and in the pebbly desert yellowish 

 plumage. In certain birds the adult individuals show no 

 special protective coloration, but the eggs and young which 

 lie on the ground have suitable coloration according to the 

 locality in which they are found. In this category are most 

 of the Waders and the other ground- breeding birds. A 

 remarkable instance, not so much of the effects of environ- 

 ment, but of adaptation, is that of the House-Martin, 

 the form breeding in Algeria having a much shorter and 

 rounder wing than the species breeding in Europe. This 

 has been evolved owing to the much shorter range of 

 migration of the African race. On the Galapagos Islands 

 and a few neighbouring islets a whole series of birds of the 

 Finch family has gradually developed. The adult males 

 are almost all of a uniform black, while the females and 

 young exhibit shades of mixed grey, brown, and buff. 

 A few have developed the black only on the fore-part of the 

 body, while others, old and young of both sexes alike, are 

 without any black at all. The nearest allies of these Finches 

 in other localities are all more or less brilliantly coloured. 



In addition to their sober and very uniform coloration, 

 the Finches of the Galapagos Islands have developed a most 

 remarkable series of bill-modifications. If we look around 

 for the reason of the remarkable development of the bills of 

 these Finches of the genus Geospiza, we at once find that 

 the most abundant and widespread vegetation on the Gala- 

 pagos Islands consists of various cacti of the genera Cereus 

 and Opuntia. On the leaves, fruit, and seeds of these cacti 



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