PETIOLATE HYMENOPTERA. 235 



however important they may be in the general 



Ammophila sabulosa. 



oeconomy of nature, cannot be regarded as ct)nnected 

 by any stronger ties with the welfare of mankind, 

 the majority are, on the other hand, equally destitute 

 of noxious qualities ; for although many of them are 

 armed with a formidable weapon, they rarely make 

 use of it unless provoked. 



It is upon the possession or non-possession of this 

 special means of offence, which depends upon a slight 

 difference in the nature of the piercing organ or ovi- 

 positor, that the petiolate Hymenoptera are divisible 

 into two principal sections, — the Terebrantia and the 

 Aculeata. The actual ovipositor indeed is composed 

 of the same parts in both these groups, consisting of 

 the three bristles already described, enclosed, as in 

 the preceding tribes, between a pair of two-jointed 

 valves; but in the Aculeata or Stinging Hymeno- 

 ptera, it is provided with a glandular apparatus, 

 which secretes a poisonous fluid; and this, when in- 

 jected into a womid formed by the horny sting, pro- 

 duces severe pain, thus rendering the ovipositor a 

 formidable offensive weapon; whilst in the Tere- 

 brantia or Borers, this organ is properly only an 

 agent of oviposition ; and although some of the species 



