52S 
MR MACGILLIVRAY ON 
casional, and in most instances merely an auxiliary charac- 
ter. These parts, however, being in general permanent and 
definite, afford, when present, very good distinctive marks. 
With regard to the spur on the wing, so remarkable in the 
Anas gamhensis, Parrajacana, Charadrius spinosus, Pa" 
lamedea cornuta^ and a few others, I may here observe, 
though this has no immediate connection with the subject, 
that, so far from being confined to a few species, as has 
hitherto been imagined, it is present in almost every bird, 
though under a very slight degree of development in the 
greater number. Of this fact, any one may very easily 
satisfy himself. It is particularly evident, or rather pal- 
pable, in the Heron tribe, among the waders in general, 
and in the Gallinaceae : nor do I remember a genus at pre» 
sent destitute of it, excepting those birds whose wings are 
so small as to be of no use for flying, such as the Apteno- 
dytes, Casuarius, and one or two more. When it has ac- 
quired so great a degree of elongation as to protrude be- 
yond the feathers, it may be used as a character ; but as 
this is very rarely the case, it cannot be of much import- 
ance as affording a character of whatever kind. 
The only universal character, namely, colour, therefore, 
being found deficient in many essential respects, and the 
others being only capable of occasional use ; I would pro- 
pose^ as being of general application, founded upon per- 
manent and essential organs, and sufficiently diversified to 
comprehend a much greater number of specific forms than 
any others, characters derived from the situation, form, 
structure, and position, of the feathers. 
The experienced botanist would smile at the idea of cha- 
racterising the species of plants by the colours of their roots, 
or stems, or leaves or petals, in preference to the form and 
position of those parts. Is it not equally unsatisfactory to 
describe the colour of a feather, of an adventitious €ircum- 
