228 BULLETIN OF THE 



compared with those fully mature, may he counterbalanced by a rela- 

 tively larger supporting surface in the wings and tail. Whatever the 

 explanation may be, the facts seem to be unquestionably as above 

 stated. 



Other variations in the plumage and in other characters depending 

 upon age, but which are liable to be confounded with individual differ- 

 entiation, might be cited, but none seem to be of sufficient importance 

 to require a special description. 



General Remarks on Individual Variation. 



After the preceding remarks on this* subject, I should perhaps state 

 expressly what I regard to be the bearing of the facts above discussed, 

 otherwise I might be understood as in a great measure discarding 

 the majority of the characters used in the diagnoses of species and 

 genera. Nothing, however, is further from my purpose. What I urge 

 is simply this : that the extent of purely individual variation is far 

 greater than has usually been recognized, and that as a result numerous 

 strictly nominal species have found their place in our systems, from 

 naturalists having mistaken these differences for true specific characters. 

 Individual variation, however, is so complicated with geographical 

 variation, that the general bearings of the whole subject will be deferred 

 till the end of the discussion of the latter topic. 



As regards the general cause of individual differences in animals, it 

 is too evidently constitutional to allow of any other hypothesis, and akin 

 to that seen in domestic animals, and which in man gives to each indi- 

 vidual his unlikeness in temperament and physical structure to all other 

 men. While individuality is so patent and so universal in the human 

 species, and scarcely less so in domesticated animals, it is one of the 

 most surprising facts in zoology that so many naturalists should have 

 entertained the idea that there is an almost total absence of it in feral 

 animals, and that the description of a single specimen will suffice for 

 that of its species. Practically, however, this has been the fact, and 

 eminently so with that large class of " species hunters," who have not 

 inaptly been characterized as "closet naturalists"; for to this class 

 and not to the field naturalists are we mainly indebted for the long 

 lists of synonymes that form so vexatious a burden to zoological 

 science. 



Certain secondary causes that share in producing individual variation 



