THE DISTRIBUTION OF SPECIES. 



213 



When Darwin was at work upon his monograph of 

 the barnacles [Cirripedia), he wrote to a friend : " Sys- 

 tematic work would be easy were it not 

 arwin s ^^^ ^.j^j^ Confounded variation, which, 



experience. 11 • 1 



however, is pleasant to me as a special- 

 ist, though odious as a systematist. . . . How painfully 

 true is your remark that no one has hardly a right to 

 examine the question of species who has not minutely 

 described many ! . . . Certainly I have felt it humil- 

 iating, discussing and doubting and examining, over and 

 over again, when in my mind the only doubt has been 

 whether the form varied from to-day or yesterday. . . . 

 After describing a set of forms as distinct species, tear- 

 ing up my manuscripts and making them one species, 

 tearing that up and making them separate, and then 

 making them one again (which has happened to me), I 

 have gnashed my teeth, cursed species, and asked what 

 sin I had committed to be so treated." 



An epoch in systematic zoology began with the study 



of the collections made by the United States Pacific 



Railway survey some forty years ago. 



Then for the first time was opened to 

 way surveys. ,. , , ., , , , 



naturalists the details of the fauna of a 



vast district under the same parallels of latitude, but 

 showing every variation in rainfall, elevation, and phys- 

 ical surroundings. The most valuable results of these 

 collections were seen in the study of birds. It was 

 found in general that each bird of the Atlantic States 

 had its counterpart on the prairies, the sage plains, the 

 mountains, and the Pacific slope. Differences were care- 

 fully sought for and found, for the followers of Professor 

 Baird allowed nothing to escape their analysis. There 

 were differences in size, in form and colour — slight in de- 

 gree, but nevertheless really existing — and these were 

 made the basis of as many distinct species. Still further 



