102 Mr Edmondston on the Colymhus Grylle^ ^c. 
pected to take place. This disappearance is general and suddeni 
for in autumn I have not observed any of this species in stages 
of plumage intermediate between the grey and black. 
The reappearance of the black in spring is also sudden, and 
the number of this species at that season appears also greater 
than in winter, and it is in spring that the different steps of 
change, from the grey to the black, are well marked. All this 
quite accords with the opinion I have adopted, and I suspect 
with hardly any other. 
If even any unequivocal instance could be produced of an 
adult guillemot assuming, during winter, the plumage of the 
young, it would not invalidate the general conclusion I have 
stated ; for still the undeniable fact would remain, and be un- 
accounted for by the hypothesis to which I object, that many 
perfectly adult birds are met with during winter ; and if excep- 
tions are admissible to the one opinion, they are equally so to 
the other. 
But the observation of the transition of the old to the plu- 
mage of the young could effectually be made, only when the 
bird was in a state of confinement, and in a few solitary instan- 
ces; yet to this experiment a valid objection might be stated, 
that from domestication producing its well known effects in vary- 
ing the plumage, and modifying the habits of animals, this ex- 
periment of itself might establish nothing general in respect to 
what regularly occurs in their wild and native state. I do not 
deny that such an experiment would furnish a strong confirma- 
tion of the opinion which I am opposing ; but still the other 
difficulties would have to be surmounted. 
We see the young passing by progressive steps to the plu- 
mage of the old, but we remark no reverse gradation. But, if 
the opinion I have endeavoured to refute be correct, the change 
in the latter case must be instantaneously and universally effect- 
ed. 
The plumage which, it is asserted, the parent bird presents in 
winter, is precisely that of its young ; and why it should assume 
this rather than any other, is perhaps a little suspicious. 
The climates where this supposed winter change is accom- 
plished are not all Arctic ones; and the opinion which conjee- 
tqres this change, states no peculiarity in this species that can 
