42 PTERYLOGRAPHY. 



remarked by Tiedemann, has an odour like musk. But that many temporary differences may 

 occur in this respect, may be learnt from the example of Upupa epqps, already mentioned. 



From these statements with regard to the oil-gland, it is easily seen that it is very well 

 adapted for the determination of natural groups of Birds, and that sometimes whole families, such 

 as the Diurnal Raptores. the Passerine, and the Columbince, and sometimes many individual 

 genera (e.g., Cathartes, Pandion, Cinclus, Uptipa, Caprimulgus, Dyspoms, and Pelccanus), may be 

 best and most certainly distinguished from their allies by its structure. 



