xlviii INTRODUCTION. 



Ichneumonidae are now primarily divided, differ only in elal^oration and 

 detail from the genera above quoted : — 



A TABLE OF SUB-FAMILIES OF THE 

 ICHNEUMONIDAE. 



(4). I. Areolet pentagonal, never entirely wanting; abdomen depressed. 



(3). 2. Post-petiole distinctly scul[)tured ; terebra not, 



or hardly, exserted Ichneumoninae* 



(2). 3. Post-petiole not or indistinctly sculptured ; 



terebra far exserted Cryptinae ^ 



(i). 4. Areolet not pentagonal, often wanting ; ab- 

 domen sometimes compressed. 



(6). 5. Abdomen laterally compressed, basally petio- 



late Ophioninae. 



(5). 6. Abdomen dorsally depressed, basally sub- 

 sessile or rarely sub-petiolate. 



(8). 7. Metanotum usually longitudinally costate ; 



terebra not exserted Tryphoninae. 



(7). 8. Metanotum not longitudinally costate ; tere- 

 bra far exserted Pimplinae. 



Nowhere probably throughout the Animal Kingdom is the instability of 

 Nature more strikingly illustrated than in the Ichneumonidae, which have 

 been termed the teeth and claws of Nature; nor is this surprising. How 

 marvellous a thing is it indeed that there should be constancy of any kind 

 in a group of insects, whose larvae are almost shapeless maggots, feeding 

 wholly immersed within the bodies of other insects ; one kind of parasite 

 very often attacking several different sorts of host, entirely devoted to 

 the varying fortunes and propensities of their living pabulum, which in 

 certain cases appertains to even different Orders. As though this were 

 not sufficient cause for instability, we are told by Kriechbaumer- that even 

 to surprise a pair of the imagines in coitn is no criterion to their being 

 specifically identical, since cross-breeding is common among allied species 

 of Ichneumons. Consequently, at the very outset, caution is necessary, in 

 that each of the sub-families enumerated above contains so great a variety 

 of forms as to be difficult of concise tabulation. Thus, in the Ichneu- 

 moninae, instances occur in which the exterior nervure of the areolet is, as 

 in Hemichneumon and Epitomus, at least pellucid; in which the wings, as 

 in a brachypterous form of Ichneinnon latrator, have no areolet ; the ab- 

 domen, as in Limerodes, compressed, or, as in Ichneumon spuriiis, with no 

 distinct petiolar sculpture ; or the terebra, as in some examples of Cratich- 

 neumon, distinctly exserted. In nearly all these vicissitudes, however, it 

 will be found that the mesosternum is entire, and not, as is invariably the 

 case in the Cryptinae, &:c., laterally sulcate. Among the Cryptinae the 

 terebra is rarely, as in Stilpnus, not exserted; the areolet, as in Mesostenus, 

 not pentagonal, or its exterior nervure, as in Hemiteles, almost entirely 



1 The Agriotypidae differ fioni the Cryptinae prininrily in having the second and third segments 

 connate and the venter chitinous. Modern authors follow Haliday in considering it to constitute 

 a family of equality with the Ichneumonidae, its single genus, Agriotypus, Curt. (Cratopus, Holnigr.), 

 connecting it with the Braconidae. 



2 Ent. Nachr. 1889, p. 290. 



