TROPICAL NATURE 



little white-eyes (Zosterops), which are probably allied to the 

 last, eat soft fruits and minute insects. 



Conclusion 



Here, then, we have an extensive group of birds, consider- 

 ably varied in external form, yet undoubtedly closely allied 

 to each other, one division of which is specially adapted to 

 feed on the juices secreted by flowers and the minute insects 

 that harbour in them ; and these alone have a lengthened bill 

 and double tubular tongue, just as in the humming-birds. 

 We can hardly have a more striking example of the necessity 

 of discriminating between adaptive and purely structural 

 characters. The same adaptive character may coexist in two 

 groups which have a similar mode of life, without indicating 

 any affinity between them, because it may have been acquired 

 by each independently to enable it to fill a similar place in 

 nature. In such cases it is found to be an almost isolated 

 character, apparently connecting two groups which otherwise 

 differ radically. Non- adaptive or purely structural charac- 

 ters, on the other hand, are such as have probably been 

 transmitted from a remote ancestor, and thus indicate funda- 

 mental peculiarities of growth and development. The changes 

 of structure rendered necessary by modifications of the habits 

 or instincts of the different species have been made to a great 

 extent independently of such characters; and as several of 

 these may always be found in the same animal their value 

 becomes cumulative. We thus arrive at the seeming paradox 

 that the less of direct use is apparent in any peculiarity of 

 structure, the greater is its value in indicating true, though 

 perhaps remote, affinities ; while any peculiarity of an organ 

 which seems essential to its possessor's wellbeing is often of 

 very little value in indicating its affinity for other creatures. 



This somewhat technical discussion will, it is hoped, enable 

 the general reader to understand some of the more important 

 principles of the modern or natural classification of animals as 

 distinguished from the artificial system which long prevailed. 

 It will also afford him an easily remembered example of those 

 principles, in the radical distinctness of two families of birds 

 often confounded together, the sun -birds of the Eastern 

 Hemisphere and the humming - birds of America ; and in 



