538 GEOGRAPHICAL VARIATION IN NORTH AMERICAN BIRDS, 
evidence afforded by mammals, which in general present climatic 
modifications parallel with those of birds. ‘salir 
Whatever may be the cause of the above modifications of struck 
ure and color at different localities, we certainly find the following 
coincidences: I. In accordance with the increase in the i 
of color in individuals of the same species from the north south- 
ward, in the northern hemisphere, the brighter colored species in 
genera represented in both the temperate and tropical regions 
occur, as a general rule, at the southward; the same fact holding 
good also for sub-families. In cosmopolitan genera, families, ettu 
at the southward, all the species that have this member enormi 
developed are tropical or semi-tropical, not only such families 
have the beak at its maximum of development, as the toucans anl 
hornbills, but in all groups in which it is unusually large, the es 
treme development is reached in the intertropical regions. £ 
In respect to the tail, with very few exceptions, all long- é 
forms attain the highest development of this member within 
near the equatorial regions. í 
The facts indicated above, in respect to the inosculation 
formerly regarded as specifically differentiated, will ev 
quire modifications of the hitherto accepted nomenclature. 
dently many of these forms are so strongly marked that 
should be in some manner recognized in nomenclatures 
admittedly of less than specific rank, Most naturalists now P 
tically recognize as species such groups of individuals as ss 
known to graduate by nearly imperceptible stages into Hes 
ar ine individuals 
similar group; and as varieties, such groups of ind 
which differ e 
in fact, already more or less generally practised. ‘eal ™ 
Finally, what is the bearing of these facts of geograp’™™ 
