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LETTER XXVII. 
ON THE INSTINCT OF INSECTS. 
Tue greater part of those surprising facts connected with the manners 
and economy of insects, of which the relation has occupied the preceding 
letters, is to be referred, I have told you, to their instinct, But what, you 
will ask, is this instinct ?—of what nature is this faculty which produces 
effects so extraordinary ? 
To this query Ido not pretend to give any satisfactory answer. As TI 
am quite of Bonnet’s opinion, that philosophers will in vain torment them=' 
selves to define instinct, until they have spent some time in the head of an’ 
animal without actually deing that animal—a species of metempsychosis’ 
through which I have never passed —I shall not attempt to explain what’ 
this mysterious energy is. It will not, however, I imagine, be very difficult 
to show what it is no¢; and some observations with this view, followed by 
an enumeration of peculiarities which distinguish the instincts of insects 
from those of other tribes of animals, and a short inquiry whether their- 
actions are guided solely by instinct, will form the substance of this letter. 
I. It is quite superfluous at this day to controvert the explanations of 
instinct adyanced by some of the philosophers of the old school, such as 
that of Cudworth, who referred this faculty to a certain plastic nature ; or 
that of Des Cartes, who contended that animals are mere machines. Nor, 
I fancy, would you thank me for entering into an elaborate refutation of 
the doctrine of Mylius, that many of the actions deemed instinctive are 
the effect of painful corporeal feelings ; the cocoon of a caterpillar, for 
instance, being the result of a fit of the colic, produced by a superabun- 
dance of the gum which fills its silk-bags, and which exuding is twisted 
round it by its uneasy contortions into a regular ball. Still less need I advert 
to the notable discovery of some pupils of Professor Winckler, that the 
brain, alias the soul, of a bee or spider is impressed at the birth of the 
insect with certain geometrical figures, according to which models its works 
are constructed—a position which these gentlemen demonstrate very satis- 
factorily by a memorable experiment in which they themselves were able 
to hear triangles. 
It is as unnecessary to waste any words in refutation of the nonsense 
(for it deserves no better name) of Buffon, who refers the instinct of 
societies of insects to the circumstance of a great number of individuals 
being brought into existence at the same time, all acting with equal force, 
and obliged by the similarity of their internal and external structure, and 
the conformity of their movements, to perform each the same actions, in 
the same place, in the most convenient mode for themselves, and least 
Inconvenient for their companions ; whence results a regular, well-pro- 
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