THE ICHNEUMONS. 237 



the second and third segments being broad but de- 

 pressed, the fourth broad and flat at its base, but 

 narrower and deeper at its hinder margin, whilst the 

 three succeeding segments are compressed laterally. 

 At the extremity of the abdomen, which is somewhat 

 truncated, or cut off perpendicularly, we see in the 

 female a short, slender, blunt spine : this consists of 

 the exserted valves between which the ovipositor is 

 enclosed. 



The general features of structure above described 

 are common to a vast number of insects, which may 

 be regarded as forming the most typical or character- 

 istic portion of the order Hymenoptera. But asso- 

 ciated with these are numerous small species, a great 

 many of which exhibit a considerable deviation in 

 the form of the body, and even in the structure of 

 some of its most important parts, from those larger 

 and more characteristic examples of the immense tribe 

 to which they are referred in common, a circumstance 

 which renders it a somewhat difficult task to give any 

 general description which shall apply equally to all the 

 members of the group. They are, however, easily 

 distinguishable from the only other tribe of petiolated 

 Terebrant Hymenoptera by the possession of an ovi- 

 positor of the structure already described, and of an 

 abdomen consisting of at least six or seven segments. 

 The antennae in many cases, as in the species referred 

 to above, are long, straight, slender, and composed of 

 numerous minute joints ; in others they are also long 

 and straight, but composed of few (13-15) joints; 

 whilst in others again, in which the number of joints 

 is also small, the organs are short, stout, and elbowed 

 at the extremity of the basal joint. In the deve- 

 lopment and structure of the wings also an astonishing 



