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REVIEW: — ILLUSTRATIONS OF INSTINCT. 
properties, to those possessed by the lowest order in creation. 
Man himself — who is beyond doubt the highest creature in the 
visible world — a genus in himself, and rightly defined by Linnaeus 
in the expressive signification of that high point of wisdom, — a 
capacity for self-knowledge, — is constituted by the plenitude of 
the natural properties which distinguish beings whose whole exist- 
ence is confined to the possession of a mere tissue ; as well as of 
those in the ascending series, whose lives are comprised in the 
separate additions of sensibility and irritability.” 
“The conclusion, then, is this: — that the essential difference by 
which one kind of animal is distinguished from another, and in 
which therefore its specific identity consists, is constituted by the 
peculiarity of tissue in its various organs, and the preponderance 
or complications of such tissue in its whole structure ; but more 
especially by the peculiarity of its nervous fabric, and the arrange- 
ment of what is called its nervous system.” 
“ In the course of this work it will be our business to trace the 
effects of the developments we have spoken of, as displayed in the 
familiar actions of animals; and chiefly in those with which we 
are best acquainted, either from their inhabiting our own country, 
or from the narratives of naturalists who have studied the crea- 
tures of distant lands in their native haunts.” “And our first 
instances will be of such actions as vary with the age of the indi- 
vidual, or with the season, before we proceed to those which are 
distinctive of the species : as by so doing we may obtain proof, 
that changes in the force or manifestation of instinct proceed from 
no other cause than fluctuations in the state of the animal body 
itself.” 
“ In some cases .... the active development of an instinct 
becomes periodic and revives again 
after a more or less definite period of suspension. This is remark- 
able in some well-known series of phenomena in the economy of 
birds, which have long excited admiration. One of these is the 
disposition to the formation of the nest, of which we shall have to 
speak hereafter. For the present, no reference is made to the 
skill employed in its structure, situation, or adaptation to use, but 
only to the formative impulse; which in some instances is so 
strong, that, when the nest is formed, instead of waiting until the 
egg is ready to be deposited, the building bird proceeds in the 
construction of others, until, at last, the further duty of using it 
for its peculiar object puts an end to its labours. This practice is 
particularly observed in the common wren (sylvia troglodytes) ; 
and it has been supposed that the true reason why this diminutive 
architect builds more than one nest is, that it has become dissa- 
tisfied with the former edifice or with its situation. But this 
