224 NORTHERN THREE-TOED WOODPECKER. 
exterior being much purer white and somewhat rounded ; the 
exterior of all is very short and rounded, and banded through- 
out with black and pure white: the tarsus is seven-eighths of 
an inch long, feathered in front for nearly half its length, and, 
with the toes and nails, dark plumbeous ; the nails are much 
curved and acute, the hind one being the largest. 
The above is a minute description of our finest male speci- 
men, with which all those we have examined coincide more or 
less. By comparing, however, this description with the detailed 
ones found in some works, we must conclude that the species 
is subject to variations in size and plumage, which, according 
to the erroneous impression given by authors, could not be 
satisfactorily accounted for by difference of sex, age, or locality : 
thus in some specimens the cervix is described white, or partly 
whitish, instead of being wholly black ; the back is also said 
to be waved with white, which is indeed the case, and with 
the cervix also, but only in young birds. There is a circum- 
stance, however, that could not be explained by supposing a 
difference of age, for while some specimens are seen with no 
appearance of white or yellow on the crown, but having that 
part, as well as the body, rich shining black, others, with a 
good deal of lemon yellow on that part, are of a duller black, 
much varied with white. As in other doubtful and intricate 
cases, these obscurities are dissipated by a close inspection and 
unprejudiced observation of nature, and we feel much gratifi- 
cation in being enabled to unveil to ornithologists the mystery 
of these diversities of plumage in this species, by merely point- 
ing out the sexual differences, as well as those originating in 
the gradual change from youth to maturity in both sexes; 
which, when understood, will not be found more extraordinary 
than in other species. 
The adult female has never been recognised by any author, 
nor, hitherto, even by ourselves, having been misled by others 
in taking the young for her; and this we have only discovered 
by inspecting a great many specimens. She is precisely similar 
