PREJUDICES OF SENSE. 159 
animals under conditions of existence not habitual to 
the species ; and which, from being casual and inci- 
dental, may be termed unnatural —that is, contrary 
to their usual natures. First, as regards the habits 
of animals; upon which, as will be hereafter seen, 
their station in the scale of nature so much depends ; 
I shall adduce a striking instance, which might have 
given rise to a prejudice of this sort, in a case 
witnessed by myself this year. A particular tree 
on the lawn, immediately opposite my library 
window, is the usual station of two grey fly- 
catchers, who have frequented it annually for the 
last five years. Those who are acquainted with 
the manners of this bird, know that it habitually 
lives seated upon trees, where it remains stationary, 
darting occasionally upon passing insects, and re- 
turning to the same twig, without perching on the 
ground. This peculiarity of habit is confirmed by 
its organisation: for, on looking to the feet of the 
bird, we see they are of such a construction as to 
incapacitate it from habitually walking, or even 
hopping, upon the ground. Nevertheless, I ob- 
served this year, for the first time, one of these 
birds in such a situation: it was upon the grass 
but once; and then, apparently, to secure an insect 
which it had wounded, but not captured, in its first 
assault. Now, had this fact been witnessed by an 
observer, not acquainted with the ordinary habits 
of the species, and ignorant of the influence which 
structure exercises upon habits, he would at once 
affirm, from his own personal experience, that the 
grey fly-catcher, and, consequently, all the species of 
the same genus, were in the habit of frequenting 
