312 Lvolution and Adaptation 
much more distinct from the western forms than these are 
from each other. 
Finally may be mentioned the curious variations in 
screech-owls of the genus Scops. This owl has two strik- 
ingly different plumages—a mottled gray and a reddish 
brown, which, although very distinct when fully developed, 
yet “are entirely independent of age, season, or sex.” There 
is an eastern form, Scops asio, that extends west to the 
Rocky Mountains. There is a northwestern form, S. kennt- 
cotti, which in its red phase is quite different from S. aso, 
but in its gray plumage is very similar. The California form, 
S. benderit, is not known to have a red phase, and the gray 
phase is quite different from that of S. aszo, but like the last 
form. The Colorado form, S. maxwelle, has no red phase, 
‘but on the contrary the whole plumage is very pale, almost 
as if bleached, the difference evident in the nestlings even.” 
The Texas form, S. masellz, has both phases, and is very 
similar to S. aszo. The Florida form is smaller and colored 
like S. asto. The red phase is the frequent, if not the 
usual, one. The flammulated form, S. fiammula, is “a very 
small species, with much the general aspect of an ungrown 
S. asto.” This is the southwestern form, easily distinguished 
on account of its small size and color from the other forms. 
These examples might be greatly increased, but they will 
suffice, I think, to convince one of the difficulty of giving a 
sharp definition to “species.” The facts speak strongly in 
favor of the transmutation theory, and show us how a species 
may become separated under different conditions into a num- 
ber of new forms, which would be counted as new different 
species, if the intermediate forms were exterminated. 
In discussing the nature of the changes that bring about 
variability, Darwin remarks: ‘‘ From a remote period to the 
present day, under climates and circumstances as different 
as it is possible to conceive, organic beings of all kinds, when 
domesticated or cultivated, have varied. We see this with 
