396 External Changes in Birds, 



the curious fact, that the common drake, and also the pin- 

 tailed and other teals, should moult their whole clothing 

 plumage (including the tail) in summer, and then again in 

 autumn ? As Mr. Waterton has well remarked on the sub- 

 ject, " All speculation on the part of the ornithologist is utterly 

 confounded ; for there is not the smallest clue afforded him, 

 by which he might be enabled to trace out the cause of the 

 strange phenomenon. To Him alone, who has ordained the 

 ostrich to remain on the earth, and allowed the bat to soar 

 through the etherial vault of heaven, is known why the drake, 

 for a very short period of the year, should be so completely 

 clothed in the raiment of the female, that it requires a very 

 keen and penetrating eye to distinguish them." [VIII. 544.} 



In one point of view, however, at least, a knowledge of 

 these changes is of considerable practical use to the naturalist ; 

 for they not unfrequently point out at once, in doubtful cases, 

 the most appropriate situation of a genus in a system, and 

 thus assist him very greatly in his endeavours to fabricate a 

 sound system of classification. Instances of this I shall not 

 here advance, as it is necessary to say something first of what 

 meaning I attach to that most hackneyed of all phrases, 

 " natural system," concerning which it is more than probable 

 that my views may very considerably, and perhaps essentially, 

 differ, from those of many who may perchance honour them 

 with a perusal. 



Under this phrase, then, two very distinct kinds of relation 

 are ordinarily blended together and confounded ; viz. the 

 adaptive relation of every organised production to the condi- 

 tions under which it was appointed to exist, and the physio- 

 logical relation subsisting between different species of more 

 or less similar organisation. These may be aptly designated 

 the adaptive system, and the physiological system ; the system 

 of relative adaptation between the earth, its productions, and 

 its inhabitants, and the system of agreements and differences 

 between the organisation of distinct races. 



To illustrate the former of these is, perhaps, superfluous : 

 it is the system by which alone the existence of one species 

 is necessary to that of another, and which binds each race to 

 its locality ; where the presence of each is alike necessary to 

 preserve the equilibrium of organic being around ; and, when 

 circumstances have changed, and the necessity for its agency 

 no longer remains, a whole race perishes, and the fragments 

 of a skeleton in the solid rock perhaps alone proclaim that 

 such had ever existed. It is the grand and beautiful, the 

 sublime and comprehensive, system which pervades the uni- 

 verse, of which the sun and planets are but a portion, and 



