Vol. XVIII 

 1901 



Clark, The Clas<iification of Birds. S^^ 



formes are quite easily defined, with many important characters. 

 A greater difficuhy still is found in the fact that certain birds, 

 such as Buceros and Co/ius, have a pterylosis so peculiar it is hard to 

 compare it with any of the types. Moreover, various birds show 

 a pattern of pterylosis, which at first glance is more like some to- 

 tally different group, than like their admittedly nearer allies. Such, 

 for example, are the Albatross, Opisthocomus, and Goatsuckers, all 

 of which are strikingly falconiform ! 



These difficulties, however, are none of them insuperable, 

 when we consider three important facts. First of all, our knowl- 

 edge of pterylography is very deficient ; Nitzsch's work is based so 

 largely on dried skins that his figures are often faulty, and conclu- 

 sions drawn from them are liable to error ; for example, his state- 

 ments regarding Podargus and the relationship between the Goat- 

 suckers and Swifts, are not borne out by examination of better 

 material than he possessed. Secondly, the study of the develop- 

 ment of the tracts has not yet received any attention, while, as I 

 have already shown, it is a most important factor in determining 

 the type of pterylosis and the value of the pterylographical char- 

 acters. Finally, the pattern of the pterylosis must not be regarded 

 as an infallible guide, but must be followed with caution. Al- 

 though it is a deep-seated character, it is by no means beyond 

 modification and even radical change, and where its leading is 

 dubious, it must be controlled by the evidence offered by other 

 characters. Some use in taxonomy has been made hitherto of 

 certain pterylographical characters, but only in a small way, and 

 it is my desire to call the attention of ornithologists to the great 

 value that the entire pterylosis pattern has in classification. 



