4S2 
OBSEllVATIONS ON SOME SPECIES 
they were apparently the same ; and hence it happens, that, 
in most collections, it is a matter of chance whether these 
birds are assigned to the proper species to v/hich they re- 
spectively belong. I have been as yet unable to perceive any 
determinate diflerence in plumage ; and the distinction in 
size being rather an individual than a specific difference, can- 
not be safely relied upon, because, as many birds vary in 
weight and dimensions, according to the^season of the year, 
and their relative condition, where there is not a very great 
and constant difference in that respect, nothing can be de- 
termined by it. I was at one time of opinion, that, in the 
Mergus merganser^ and its female the Mergus castor^ the 
bill was uniformly deeper at the base laterally, and the 
nostrils further removed from the frontal feathers, that is 
nearer the point, than in the Mergus serrator. This dis- 
tinction I believe is general between the full grown and 
perfectly matured birds of both sexes of these species ; but 
I am in doubt whether it holds good in regard to the 
younger individuals 
* I am aware of the frequent discussions which have been entered into 
regarding the structure of the windpipe in this genus, though I have taken 
no notice of these in the preceding paper, being unwilling to venture upon 
any thing like anatomical detail, when the points in question can be deter- 
mined by reference to external characters. I may mention, however, that, 
notwithstanding the frequent assertion to the contrary, by those who have 
endeavoured to prove the distinction between the male Dundiver and the 
Goosander to be founded on anatomical differences, no internal distinction 
whatever exists between these birds. The appai-ent difference in the shape 
and formation of the trachea, and the contradictory statements and errone- 
ous conclusions to which it has given rise, result simply from the circum- 
stance above alluded to, of which anatomists were not aware, namely, the 
resemblance which the young males and females of the Red-breasted Mer- 
ganser bear to those of the Goosander. The trachea of the male Goos- 
OTder possesses two swellings, or enlargements, in its course, besides the 
