Birds. 



8487 



robes with which Nature has alike decked them, all authors on Orni- 

 thology had placed the Trochilidae near the Nectarinida3 and Meli- 

 phagidae, till Prince Bonaparte, in his ' Conspectus Generum Avium/ 

 published in 1850, separated them widely from these groups, and 

 placed them immediately after the swifts (Cypselidse). In 1856, in a 

 paper on the " Natural Arrangement of Birds," published in the 'Annals 

 of Natural History ' (p. 193), I classed them as a very aberrant group 

 of Fissirostres, and believe I was the first writer, at least in England, 

 to give any reasons for so placing them. 



Before proceeding to state what these reasons are it is necessary to 

 make a few observations on some important principles of classification. 

 It is now generally admitted that for the purpose of determining obscure 

 and distant affinities we should examine those parts of an animal 

 which have little or no direct influence on its habits and general 

 economy. The classificatory value of an organ is in inverse proportion 

 to its adaptability to special uses. By this means we shall penetrate 

 the disguise of external form as adapted to similarities of food and 

 habits, and arrive at the true and essential differences that underlie 

 them. We thus determine that the Cetacea are not fishes, though 

 judging from external form and habits alone we should certainly so 

 class them, because the essential mammalian characters, which are 

 anatomical and physiological, remain highly developed. So, though 

 there are Marsupials which take upon themselves the exact form, habits 

 and mode of life of Rodents or Carnivora, yet minute details of struc- 

 ture in the skull and skeleton, and their physiological peculiarities are 

 universally held to separate them completely from these orders. 

 Among birds the hornbills and the toucans may be said to have the 

 same general form, to agree strikingly in their enormous bills, in their 

 general habits, their food, and their mode of taking it, — yet peculiar- 

 ities in the structure of the feet, of the plumage, and more particularly 

 of the skeleton, show that they have no real affinities, the former 

 approaching the kingfishers and the latter the cuckoos. 



On the other hand we often find peculiarities of organization, which 

 seem specially adapted to the mode of life, become diminished or alto- 

 gether lost in certain aberrant species of whose affinities notwithstand- 

 ing there has never been any doubt. For example, the woodpeckers 

 are most strikingly characterised by the extensile tongue with os hyoides 

 prolonged over the head, exactly as in hummers, and also by the rigid 

 and pointed tail ; but in one group (Sasia and Picumnus) the tail 

 becomes quite soft, while the tongue remains fully developed; in 

 another (Meiglyptes brunneus) the characteristic tail remains while the 



