MUSEUM OF COMPARATIVE ZOOLOGY. 243 



being attached to trivial differences, so that assumed species were fre- 

 quently based solely on either individual or climatic variation, but 

 oftener on both combined. 



As the rage for describing new species increased, differences seemed 

 alone to be sought ; and so long as a given species was usually deemed 

 sufficiently represented, even by the best ornithologists of the day, by 

 a single pair,* the subject of individual and climatic variation was neces- 

 sarily almost wholly neglected, the custom of many naturalists being to 

 describe species from single specimens, as though all the representatives 

 of a species were cast after an unvarying pattern. As the number of 

 specimens of well-known species increased in our large museums, it was 

 soon seen that some of the supposed most reliable diagnostic features 

 were subject to considerable variation. The collections brought 

 together from various parts of the continent by the Pacific Railroad 

 surveying parties and from other sources, and the reports published 

 thereon, formed the beginning of a new era in the history of the orni- 

 thology of North America, and in ornithological science. The facts thus 

 disclosed in respect to geographical range, and individual and climatic 

 variation, opened new fields of inquiry. Old theories and blind adher- 

 ence to authorities, however, still impeded progress and led to frequent 

 inconsistencies, which only time and further investigations could correct. 

 Hence has gradually dawned the fact of the existence of a range of 

 individual variation previously unsuspected, and of general laws of 

 climatic variation, the full scope of which, as bearing upon the character 

 of species, is yet to be determined. 



Nearly half a century since it was discovered that the North 

 American representatives of what were then commonly regarded as 

 circumpolar species could not in all cases longer be regarded as identical 

 with the European. Further comparisons showed that in most cases 

 of the supposed circumpolar distribution of species, specimens from the 

 Old "World and the New could be more or less readily distinguished, 

 yet the differences were in most cases slight, more or less inconstant, 

 and not unfrequently due more to differences in the latitude whence the 

 specimens came than to other causes. Yet a precedent for specific 



* Not many years since amateur ornithologists were kindly informed, by ono of the 

 leaders in the science of ornithology, that his collection of the birds of a certain country, 

 numbering over two thousand species, required for their convenient storage a space 

 equal to only about one hundred cubic feet, the specimens averaging less than two to a 

 species 1 



