INTRODUCTION. xlvii 



(3). 8. Front wing with no discoidal nervures. 

 (10). 9. Antennae of c? with some ring-Hke joints; 



venter emitting terebra Chalcididae. 



(9). 10. Antennae of c^ with no ling-hke joints ; 



anus emitting terebra Proctotrypidae. 



Family. ICHNEUMONIDAE. 



It is of this important family, — so well known superficially from long 

 pre-Linnean times, on account of its species' wonderful economy and 

 instinct, and even yet one of the least critically elucidated, because of 

 the extreme specific similarity, individual variation and the consequent 

 difficulty of discrimination, — that I propose to treat in the following pages. 

 Typical examples of the sub-families are most distinct and unmistakable, 

 but the outlying genera, such as Megastylus, Atractodes, Exetastes, &c., 

 are difficult to correctly place in natural sequence ; and, although super- 

 ficially abundantly distinct, the most widely separated of the Ichneumonidae 

 will be found to differ comparatively little from one another structurally. 

 Hence has arisen a great impediment to their study, even now among 

 the most neglected of the whole Insecta, which fact is the more surprising, 

 until investigated, on account of the large size and striking appearance of 

 its more conspicuous members, especially of those herein described. 



It was, as I have already remarked, De Geer who first proposed dividing 

 the Terebrantia into sections, corresponding with the sessility of the basal 

 abdominal segment upon the metathorax. This method was elaborated by 

 Schrank, in 1802, and the diversity of the neural structure supplemented 

 thereto, by Jurine, in his Nouvelle Methode de Classer les Hymenopteres, 

 in 1807. In i8r8, Gravenhorst and Nees von Esenbeck drew up the 

 first at all satisfactory system of natural sequence ; and this was followed 

 by the former's Ichneumonologia, so full of thought, industry and un- 

 avoidable errors as to have required nearly a century's elucidation. It 

 deals exhaustively with the Ichneumonidae as understood to-day, to the 

 exclusion of all other terebrant Hymenoptera, and divides them into 

 species with compressed or depressed, secondly petiolate or sub-sessile, 

 abdomens ; the shape of the head ; presence or absence of the areolet ; 

 extent of exsertion of the terebra ; shape and convexity of the scutellum, 

 and many other pertinent points, evolving therefrom twelve genera and 

 sixty sub-genera. The principal of the former were Ophion and Banchus 

 alone having the abdomen compressed ; Pimpla and Xorides, with the 

 al)domen sub-sessile and the terebra exserted ; Tryphon and Bassus, with 

 abdomen sessile, but terebra concealed ; Cryptus, with petiolated abdomen 

 and terebra exserted ; and, lastly. Ichneumon, with petiolated abdomen, 

 but terebra concealed. These genera constitute the basis of modern 

 classification ; and, although the sexes were at that time to a large extent 

 considered distinct species — a common error, first indicated by Schrank, in 

 1 781, — it would be quite impossible to here refer to the subtle and gradual 

 modifications which have since been found from time to time to be 

 needful, or to revert to the many hundreds of genera into which the 

 above sixty have more recently been sub-divided, upon the discovery of 

 new forms, or of points of divergence in the old ones, overlooked by their 

 erectors. It will be seen that the following sub-families, into which the 



