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Fan: 5, 1871] 
NATURE 
183 

of the special observation on which the generalised state- 
ments are founded. We are, therefore, unable to tell 
how much is fact and how much inference ; and, what is 
probably the result of careful life-long observation fails 
to produce that effect of reality which a more direct 
narrative style would have given to it. 
however, he gives us actual observations ; as when he 
proves that animals can count, by stating the fact that in 
In a few cases, | 
order to destroy crows, which were destructive to game, | 
a hut was made at the foot of a tree where there was a 
nest, in order to shoot the old birds when they returned | 
to their young. It was found, however, that after the 
first time the man was always watched into the hut, and | 
the crows would not return till he had left it or till night. | 
To deceive them two men went to the door of the watch- 
house, one entering and the other passing on, but the 
crows would not come. The next day three went and two 
passed on, but still with no effect; and it was not till 
five or six went and all but one passed on, that they were 
deceived, being unable to count so many. 
M. Leroy appears to reject altogether what is commonly 
termed Instinct, maintaining that the word should be 
applied only to those acts which are the direct con- 
sequences of organisation, such as the grazing of the 
stag, or the flesh-eating of the fox; but not to the ex- 
pedients to which those animals resort in the gratification 
of their natural wants, which are due to sensation, obser- 
vation, memory, and experience. To the objection that 
many animals perform complex operations perfectly well 
without experience, and always in the same manner, he 
replies that in many cases the fact is not so, He main- 
tains, for instance, that there is a distinctly perceptible 
inferiority in the nests made by young birds, thus antici- 
pating the observation of the American Wilson; and 
further remarks that the best constructed nests are formed 
by birds whose young remain a long time in them, and 
thus have more opportunity of seeing how they are made 
He says that the nests of young birds are ill-made and 
badly situated ; and that the defects. of these first con- | 
structions are remedied in time, when their builders have 
been instructed by their sense of the inconveniences they 
have endured. He maintains that nests of:the same species 
of bird differ as much as human dwellings, and that of 
a hundred swallows’ nests no two are exactly alike; and 
he imputes to want of long-continued observation our 
failure to discover improvement in them ; a want which 
curiously enough, has been remedied by M. Pouchet, 
who has found a decided improvement in the nests of 
swallows at Rouen during his own lifetime. Our author 
has also some excellent remarks on hereditary habit, as 
strikingly shown in the case of many of our sporting dogs, 
and which, he believes, in wild animals is often mistaken 
for instinct ; and he concludes that “It is possible that the 
actions which we see performed by some animals, in- 
dependently of the teachings of experience, are the fruit 
of a knowledge of very ancient date, and that in former 
times a thousand trials, attended with more or less success, 
have finally led to the attainment of the degree of per- 
fection which we see manifested in some of their works at 
the present day.” 
The migrations of birds, also, he maintains are the 
result of no blind instinct, but of instruction handed | 
down fyom generation to generation. He says, “Let us, 

take the swallows as an example which every one can 
observe. In the first place, their departure is always 
_ preceded by assemblages, the frequency and duration of 
| purpose. 

which can leave no doubt that their object is to effect all 
the necessary preparations for a voyage undertaken by 
creatures who have the faculty of sensibility, and of under- 
standing one another, and who are united for a common 
The incessant and varied twittering which 
reigns in these assemblies, clearly indicates communica- 
tions and orders, indispensable for the numerous offspring 
of the year. They must stand in need of preliminary in- 
struction, constantly repeated, to prepare them for the great 
event. Frequent trials of flight are no less indispensable, 
and are often followed by a repetition of previous lessons, 
which makes our roofs and chimneys ring again. As- 
semblies of men who should speak a foreign language 
could not give more evident signs of a similar project. 
But there is a more convincing proof than this analogy 
that these migrations are not the result of a blind and 
mechanical inclination. When, at the time fixed upon 
for the flight, which cannot, owing to weather, be retarded 
without compromising the welfare of the whole species, 
some, and even a large number of indviduals, are too 
young to follow the rest, they are left behind and remain 
in the country. But it is in vain that they reach maturity ; 
the supposed attraction towards a certain region dees not 
affect them, or too slightly to enable them to gratify it. 
They perish, the victims of their ignorance, and of the 
tardy birth which made them unable to follow their 
parents.” 
The letters on Man, which are curiously mixed up 
with those on animals, are neither so interesting nor so 
well reasoned. Their object is mainly to deduce the 
complex phenomena of human existence from the two 
principles of “the love of ease” and “ enmuz,” which being 
antagonistic, lead men to all kinds of expedients to secure 
the one or escape from the other. These, with sympathy, 
| which he considers the pre-eminently human emotion, are 
made to explain most of the facts of man’s mental nature. 
The work is written throughout in a pleasing and simple 
style, and exhibits to us a loving student of nature who 
observed and thought for himself, and who, in many of his 
conceptions, was far in. advance of the great philosophers 
of the last century, among whom he lived. 
ALFRED R, WALLACE 


OUR BOOK SHELF 
UYse.qud Limit of the Imagination in Science. 
Tyndall. (London: Longmans and Co.) 
Tuls is a second edition of Dr. Tyndall’s Discourse 
at the meeting of the British Association at Liverpool, 
To it is now appended his Address as president of Section 
A of the British Association at the Norwich meeting. 
This was analysed by Dr. Clark Maxwell at a later 
meeting (see NATURE, Liverpool Meeting, Address to 
Section A). There is also added a short Essay from the 
Saturday Review, with the quaint title of “ Earlier 
Thoughts,” suggesting the irrepressible “Country 
Parson,” A.K.H,B. Another curious addition is a selec- 
tion of favourable, unfavourable, and often ridiculous 
critiques of various parts of his discourse ; which reveak 
the existence of a strange state of things in the arcana of 
editorial dens. : : 
One og tivo trenchant notes are appended to the Dis- 
By Prof. 
