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 
for this confounded variation, which, 
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. 
on eer ae Then for the first time was opened to 
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 
Darwin’s 
experience. 
