4 INTRODUCTION. 



refers. When we find the authors of the most imposing systems 

 making the most absurd statements in almost every page, we 

 ought to become diffident of our own powers, and reflect that 

 the mysteries of creation are scarcely to be understood even by 

 him who to great acuteness adds great perseverance and great 

 humility.* 



IVIuch of the discrepancy of opinion respecting the limits of 

 the genera and families of birds arises from forgetfulness of the 

 fact that species alone exist in nature. Most persons acknow- 

 ledge this truth when it is forced upon them ; but few act 

 under its impression. A species, composed of individuals of 

 two sexes, capable of producing similar individuals, varying 

 however within certain, but hitherto undefined limits, and ca- 

 pable of continuing the race, which remains the same for ages, 

 and of which the varieties, when placed in ordinary circum- 

 stances, tend to return to the original type, is all that we can 

 consider as having a positive existence. It is merely because 

 species are so numerous, and our faculties so limited, that we 

 throw them into ideal groups, for the purpose of facilitating 

 our recollection of their forms and qualities. Species are more 

 or less allied to each other ; thus, a Raven is very similar to a 

 Carrion Crow, less so to a Magpie, and in a much smaller 

 degree to an Auk or a Penguin. The alliances exhibited 

 between species give rise to the idea of connecting them in 

 various degrees ; but the limits of the groups thus formed being 

 undefined, it is not in the nature of things that those arbitrarily 

 fixed by one man should be acknowledged by all others. It is 

 very evident that genera, families, orders, and all the mediate 

 sections of a class, must ever remain fluctuating, and that dis- 



* " The structure of birds," says tlie author of a recent work, " adapts 

 them for inhabiting an element from which quadrupeds, and even man, is ex- 

 cluded." One naturally asks, What element can this be ? man lives in air, 

 walks on earth, and swims in water ; so do quadrupeds and birds. Othei-s 

 inform us that the Raptores, or birds of prey, have the body very muscular ; 

 the upper mandible the longest ; and that they nidificate in lofty situations : 

 whereas the body of a Pheasant is greatly more muscular than that of a Sparrow- 

 hawk ; the upper mandible of a Parrot or an Albatross, in fact, of almost all 

 birds, is the longest ; and the Merlin nestles on the ground, as do the Moor 

 Buzzard and the Henharrier. 



