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CHAPTER XVIII. 
divers: THE CRESTED, RED-NECKED, HORNED, AND EARED 
GREBES — THE DABCHICK. LOONS : THE RING-NECKED, 
BLACK-THROATED, AND RED-THROATED LOONS. 
AT the commencement of our account of the Water 
Birds, it will be remembered we stated that they were 
arranged in three great divisions, viz.. Sifters, Divers, and 
Plmigers. We have now come to the second of these divi- 
sions, called by naturalists Urinatores, These are birds 
especially adapted for diving and swimming, both in and on 
the water, feeding essentially on fishes obtained in the 
living state, and pursuing their prey in its native element, 
into which they dive for that purpose, not from on wing, 
but when scattered on its surface. True, the Mergansers, 
and other of the birds already described, do this ; but most, 
if not all, of these feed occasionally on other substances than 
fish, and have natural afiSnities with birds which could not 
well be placed in this division. As we have before had 
occasion to observe, in those natural-history arrangements 
which are necessary, the line of demarcation between dif- 
ferent orders and lamilies cannot always be distinguished, 
especially by those unacquainted with anatomical structure 
and other circumstances which guide systematists, whose 
judgement we may not question. Pass we then to the Divers, 
of which order but nineteen species occur in Britain, although 
most of them are exceedingly numerous in individuals. 
Macgillivray divides them into four families, of which we 
take first the Grebes. 
