478 OBSERVATIONS ON SOME SPECIES 
ment drawn from one species, and applied to another, could 
not in any other case be so securely relied upon. 
It will be perceived that I have adopted that opinioUj 
which maintains that there is no specific distinction between 
the Mergiis Merganser and the Mergus Castor^ but that 
they form the male and female of the same species ; and I 
think I have done away with any objection in respect to 
the disagreement in plumage, by pointing out the same 
distinction, not only as existing in, but as characterising 
the sexes of the other nearly allied species, thus converting 
it from a specific difference, into a trait of generic resem- 
blance and agreement. 
I have examined all the British and French species of 
the genus, and likewise an American species, called the 
Mergus citciillatus ; and in the plumage of these I have 
found the same sexual distinctions existing as we perceive 
between the Goosander and the Dundiver, the colouring 
of the males being like the former, of the females like the 
latter. It was this general survey, and the uniform sexual 
contrasts pointed out by it, which confirmed me in the be- 
lief, that no specific distinctions were to be found between 
the castor and the merganser. 
The chief arguments which have been adduced in favour 
of these birds being distinct, are as follows. 
1,?^, The much greater abundance of the Castor^ or 
Dundiver,^ than of the Merganser, or Goosander, there 
being, according to Dr Heysham, from ten to fifteen of 
the former to one of the latter. Now that the former (re- 
garded as the female) should be much more numerous 
than the latter (considered as the male), is in perfect agree- 
ment with what I should have anticipated to be the case, 
from the fact, established by many recent observations in 
ornithology, that these birds (in common with almost all 
