244 BULLETIN OF THE 



separation in such cases having been established by recognized author- 

 ities, it was followed till all the land-birds and a large proportion of 

 the water-birds of the two continents were separated, in many cases, it 

 would appear, on purely theoretical or geographical grounds.* When 

 the comparison was carried to specimens of continentally di-tributed 

 species from distant localities, differences between these were also de- 

 tected, and the theory of specific diversity assumed, till the Pacific 

 representatives of such species were separated from the Atlantic ones, 

 and in like manner the southern from the northern, and those of 

 particular areas, as insular, peninsular, and interior basins, from the 

 others. In some cases such separations were of course properly made, 

 but a high percentage of such forms are now found to intergrade through 

 specimens from the intermediate localities. 



Not a few of the species of our faunal lists have been based on, and 

 are still only known from, single specimens, and often on differences 

 manifestly within the range of individual variation ; others represent 

 local races, which only appear distinct when extremes alone are consid- 

 ered, the intermediate stages being unknown or ignored. The increase of 

 synonymes from this fruitful source appears to have not yet culminated, 

 a large proportion of the "new species" now annually described being 

 but slight local differentiations of previously known specific forms, from 

 which they often differ only in being a little smaller, a little darker or 

 brighter colored, and in the individual peculiarities of the single specimens 

 on which some of them are based. In many cases this process of ultra 

 subdivision has furnished stepping-stones to later generalizations ; in too 

 many other cases it has been in its results only unmitigatedly injurious. 



So large a proportion of the commonly recognized species are virtu- 

 ally nominal, or rest on a false basis, it is not surprising that in the 

 reaction consequent upon, a fuller knowledge of the birds of this conti- 

 nent, which has already commenced, the reality of species should be to 

 some extent ignored. Whether, however, species are considered as 

 entities or only as arbitrary inventions, convenience demands some 

 established definition of them. 



* Audubon, writing in 1838 (Orn. Biog., Vol. IV, p. 608), refers to the Prince of 

 Musignano (by whom a large part of the circumpolar and cosmopolitan specie* were 

 separated into numerous assumed species) as *' having altered his notions so far as to 

 seem desirous of proving that the same species of birds cannot exisfc on both the con- 

 tinents"; and there seems to have, been good reason for the remark, only instead of 

 proving them distinct, he in most cases merely assumed them to bo so. 



