PDF - Wallace Online

TROPICAL NATURElittle white-eyes (Zosterops), which are probably allied to thelast, eat soft fruits and minute insects.ConclusionHere, then, we have an extensive group of birds, considerablyvaried in external form, yet undoubtedly closely alliedto each other, one division of which is specially adapted tofeed on the juices secreted by flowers and the minute insectsthat harbour in them ;and these alone have a lengthened billand double tubular tongue, just as in the humming-birds.We can hardly have a more striking example of the necessityof discriminating between adaptive and purely structuralcharacters. The same adaptive character may coexist in twogroups which have a similar mode of life, without indicatingany affinity between them, because it may have been acquiredby each independently to enable it to fill a similar place innature. In such cases it is found to be an almost isolatedcharacter, apparently connecting two groups which otherwisediffer radically. Non- adaptive or purely structural characters,on the other hand, are such as have probably beentransmitted from a remote ancestor, and thus indicate fundamentalpeculiarities of growth and development. The changesof structure rendered necessary by modifications of the habitsor instincts of the different species have been made to a greatextent independently of such characters; and as several ofthese may always be found in the same animal their valuebecomes cumulative. We thus arrive at the seeming paradoxthat the less of direct use is apparent in any peculiarity ofstructure, the greater is its value in indicating true, thoughperhaps remote, affinities while ; any peculiarity of an organwhich seems essential to its possessor's is wellbeing often ofvery little value in indicating its affinity for other creatures.This somewhat technical discussion will, it is hoped, enablethe general reader to understand some of the more importantprinciples of the modern or natural classification of animals asdistinguished from the artificial system which long prevailed.It will also afford him an easily remembered example of thoseprinciples, in the radical distinctness of two families of birdsoften confounded together, the sun -birds of the EasternHemisphere and the humming - birds of America ;and in