23 
as that which was subsequently and independently enunciated by Mr. W al- 
lace in Nature X, p. 459 (1874). Thus, to quote from the essay: »During 
the long course of ages, let valleys become converted into estuaries and then 
into wider and wider arms of the sea; and still I can well believe that the 
impulse (originally due to seeking food), which leads the pinioned goose to 
scramble northward, would lead our bird over the trackless waters; and that, 
by the aid of the unknown power by which many animals (and savage men) 
can retain a true course, it would safely cross the ocean covering the sub- 
merged path of its ancient journey,« 
The next topic considered is that of instinetive fear. Many facts are 
given, showing the gradual acquisition of such instinctive fear, or hereditary 
dread, of man, during the period of human observation. These facts led 
Mr. Darwin to consider the instinct of feigning death as shown by sundry 
species of animals when in the presence of danger. Seeing that »death is an 
unknown state to each living creaturec, this seemed to him »a remarkable 
instinct, and accordingly he tried a number of experiments upon the sub- 
ject with insects, which proved that in no one case did the attitude in which 
the animal »feigned death«, resemble that in which the animal really died; 
so that the instinct really amounts to nothing else, in the case of insects at 
all events, than an instinct to remain motionless, and therefore inconspi- 
cuous, in the presence of danger. From the facts given with regard to cer- 
tain vertebrated animals, however, it is doubtful how far this explanation 
can be applied to them. 
A large part of the essay is devoted to »Nidification and Habitationc, 
with the object of showing, by an accumulation of facts, that the complex 
instincts of nest-building in birds and of constructing various kinds of habi- 
tations by mammals, all probably arose by gradual stages under the directing 
influence of natural selection. 
Among other »miscellaneous remarks« on instincts in general he notes: 
First the variability of instinct is proved by sundry examples; next the fact 
of double instincts occurring in the same species; after which, »as there is 
often much difficulty in imagining how an instinct could first have arisen«, 
it is thought »worth while to give a few, out of many cases, of occasional 
and curious habits, which cannot he considered as regular instincts, but 
which might, according to our views, give rise to such«. Finally, cases of 
special difficulty are dealt with; these may be classified under the follow- 
ing heads: — 1) Similar instincts in unallied animals; 2) dissimilar in- 
stincts in allied animals; 3) instincts apparently detrimental to the species 
which exhibit them; 4) instincts performed only once during the lifetime of 
an animal; 5) instincts of a trifling or useless character; 6) special difficulties 
connected with the instinct of migration; 7) sundry other instincts presenting 
more or less difficulty to the theory of natural selection. 
Mr. Darwin concludes: — »We have in this chapter chiefly considered 
the instincts of animals under the point of view whether it is possible that 
they could have been acquired through the means indicated on our theory, 
or whether, even if the simpler ones could have been thus acquired, others 
are so complex and wonderful that they must have been specially endowed, 
and thus overthrow the theory. Bearing in mind the facts given on the ac- 
quirement, through the selection of self-originating tricks or modification of 
instinct, or through training and habit, aided in some slight degree by imita- 
