376 ITS REMAINING THE SUMMER. 
wherever man has fixed his abode, or extended 
his domains; and though prima facie we might 
imagine the actions and habits of animals to 
be as undeviating and determinate on all points 
as are the fundamental laws of their organizations 
and constitutions, we find on the contrary a 
corresponding alteration and conformity of action 
in them to suit our intrusions on their ter¬ 
ritories, our planting, our tillage, our building, 
and all our various operations on and perversions 
of Nature. In civilized and cultivated territories 
scarce an animal moves but it encounters alterations 
of our making; and though the lower tribes can 
experience but slight impediments, and can have 
to adapt themselves thereto only in a very minor 
degree, yet the higher tribes must certainly employ 
some portion of thought at times to overcome these 
hinderances ; and as before said, if instinct were so 
confined and restrained a power as usually con¬ 
ceived, these alterations in Nature would infallibly 
disarrange all their proceedings. Judging by the 
analogy of a vast number of instances of departure 
from accustomed actions, and by the anomalies of 
individual cases as contrasted with the species 
taken in the aggregate, we conclude that the in¬ 
stances of the Grey Wagtail’s breeding in Devon 
are determined purely by choice, and are not de¬ 
pendent on any human causes or interferences, and 
that these are also cases showing that instinct is not 
so very constrained a faculty, but involves a certain 
portion of thought and volition. If the instincts 
implanted in the Grey Wagtail were of a definite, 
precise, constrained, and unalterable nature, they 
would necessarily pervade every member of the 
species ; and so far from any pair of birds choosing 
to stay the summer with us, while all their fellows 
were preparing to migrate, no inducement of food 
ever so great, nor even any accidents or ailments 
