408 Mr. A. R. Wallace on the Arrangement of the 



found to accord with a striking anatomical feature_, and to 

 mark out an important natural group of families, it was not 

 applied to the more extensive series of families which remained, 

 and whose arrangement has continued to this day in a most 

 unsettled state. Hardly any two ornithologists agree as to 

 the order in which these families most naturally follow each 

 other; and even in the most recent classifications the pecu- 

 liarities of the first primary are deemed of so little importance 

 that birds which markedly differ in this respect are sometimes 

 placed in the same or in adjacent families or, even, genera. 

 After repeated attempts, during many years, to group natu- 

 rally the families of Passeres, I have recently come to the con- 

 clusion that variations in the number and development of the 

 primary quills indicate deep-seated affinities, and furnish the 

 best, because the most simple and practically convenient, 

 means for the further subdivision of this extensive Order. 

 The fact that similar peculiarities of wing- structure run 

 through whole series of families which are undoubtedly re- 

 lated, is a clear indication of the importance of these cha- 

 racters ; and we shall, I think, find that if we follow them 

 out cautiously, and give due weight in doubtful cases to other 

 proofs of affinity, we shall be led to a grouping of this vast 

 and complex mass of birds which avoids many of the diffi- 

 culties that have hitherto beset their classification, and ac- 

 cords in a remarkable manner with the main featui'es of their 

 geographical distribution. 



Four types of wing are distinctly recognizable among the 

 Passeres. Pirst and most numerous are those with 10 pri- 

 mary quills, the first of which is greatly reduced in size ; then 

 we have the American series, in which the first primary is well 

 developed ; and a small Old- World series, in which it is rudi- 

 mentary; and lastly a series in which the first primary is 

 aborted, and which thus possesses only 9 primaries. These 

 differences may be tabulated as follows ; but it is found most 

 convenient to arrange them in the order of the appended 

 numerals, as we thus pass most easily from one series to 

 the other, and that order best accords with existing arrange- 

 ments : — 



