7 Patmer, The Maryland Vellow-throat. 233 
Bay only ¢richas is found. At Smith’s Island the summer resi- 
dents are rather large ¢richas and quite unlike those from Virginia. 
Beach which is but 20 miles across the mouth of Chesapeake Bay. 
Intergradation must occur through the region about the mouth of 
the James River, in fact specimens from near Suffolk, just outside 
the Dismal Swamp, are less like vescoe than those in the swamp. 
Occidentalis presents some variation in the direction of other 
forms. The birds of the great California and Rio Grande valleys 
are greener above and have the sides of the body more exten- 
sively yellow than in other examples. These lowland individuals 
_ trend in the direction of melanops. 
The differences between occidentalis and melanops are blended 
in an adult male taken by Dr. E. A. Mearns at Fort Hancock, 
Texas, June 13, 1893, which is undoubtedly a geographical inter- 
grade (No. 134393 U.S. N. M. Coll.). In this specimen the 
wing is 58 mm.; tail, 54mm.; culmen, 11 mm.; tarsus, 22 mm. 
There is much yellow mixed with the worn white crown band, 
and its appearance readily suggests both occidentalis and melanops 
_ Variations. 
‘“Tndividual variation” as usually understood and spoken of 
is simply a phrase to denote our ignorance of the precise relations 
of individuals to their environment, their ecology. It also gener- 
ally covers differences of age. As I have shown, most of the 
differences in the species ¢vichas are purely zoogeographical, a 
result of their peculiar and positive relation to their environment, 
both in summer and winter, in fact the various forms are products 
of their own peculiar environments. There is little true individual 
variation, that is, variation from the average in the same locality. 
A few specimens, here and there, of ¢vichas have a wider and 
whiter area of ashy on the head. This is simply due to a wider 
absence of a maximum amount of pigment in the growing feather, 
caused probably by a local lesion or lapse of pigment (= equal 
food change) while the feathers were growing. Sometimes a 
male shows a lightening of the yellow of the throat, but such 
specimens are rare. More variation is noticeable in the females 
of ¢richas, less so in brachidacty/a, a few being entirely destitute of 
