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LETTER XXVII. 



ON THE INSTINCT OF INSECTS. 



The 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 I do not pretend to give any satisfactory answer. As I 

 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 being 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 not; 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 advanced 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, 

 1 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 superabundance 

 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 con- 

 structed — a position which these gentlemen demonstrate very satisfactorily 

 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 socie- 

 ties 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 incon- 

 venient for their companions ; whence results a regular, well-proportioned, 

 and symmetrical structure: and he gravely tells us that the boasted hex- 



