MEANS OF DEFENCE OF INSECTS. 



Jiar scent. Some dipterous insects though these in ge- 

 neral neither offend nor delight us by it are distin- 

 guished by their, smell. Thus Mesembrina mystacea, a 

 fly that in its grub state lives in cow-dung, savours in 

 this respect, when a denizen of the air, of the substance 

 in which it first drew breath a . And another (Sepsis 

 cynipsea,) emits a fragrant odour of baum b . I have not 

 much to tell you with respect to apterous insects, except 

 that lulus terrestris, a common millepede, leaves a strong 

 and disagreeable scent upon the fingers when handled c > 

 Most of the insects I have here enumerated, probably, 

 are defended from some enemy or injury by the strong 

 vapours that exhale from them; and perhaps some in the 

 list produce it from particular organs not yet noticed. 



I shall next beg your attention to those insects that 

 emit their smell from particular organs. Of these, some 

 are furnished with a kind of scent-vessels, which I shall 

 call osmateria , while in others it issues from the intes- 

 tines at the ordinary passage. In the former instance the 

 organ is usually retractile within the body, being only ex- 

 erted when it is used : it is generally a bifid vessel, some- 

 thing in the shape of the letter Y. Linne, in his gene- 

 ric character of the rove-beetles (StaphylinicUe\ mentions 

 two oblong vesicles as proper to this genus. These or- 

 gans, which are by no means common to the whole ge- 

 nus, even as restricted by late writers, are its osmateria, 

 and give forth the scent for which some species, particu- 

 larly Ocypus brunnipes, are remarkable. If you press 

 the abdomen hard, you will find that these vesicles are 



a De Geer, vi. 134. Meigen Dipt. v. 12. 



b De Geer, vi. 135. 33. c Ibid. vii. 581. 



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