18 ICllXEUHONlD.'E, 



OiiuER HYMENOPTERA. 

 Family ICHNEUMONIDiE. 



About half the known Indian forms of this important family- 

 are dealt with in the following ])ages. These insects were well 

 known superficially long before the time of Liuuseus, on account 

 of their wouderful habits and instincts ; still even yet the iamily 

 has received but little attention, because the extreme specific 

 similarity, in coujuuctiou with much individual variation, often 

 renders the discrimination of the species a matter of considerable 

 ditficulty. Typical examples of the various subfamilies are most dis- 

 tinct and unmistakable, but the outlying genera such as Me<jastylus, 

 Atraciodes, and Exetastes are difficult to place correctly in natural 

 sequence ; and however distinct they may appear superficially, the 

 most widely separated and incongruous of IchxeumonijjyE will be 

 found to differ comparatively little one from another in their 

 structure. 



De Geer was the first author to propose dividing the Terebrantia 

 or Entomophaga into sections depending on the sessility or other- 

 wise of the basal abdominal segment upon the metathoi-ax, whicli 

 method was elaborated by 8chrank in 1802, and further supple- 

 mented with characters drawn from the neuration by Jurine in 

 his ' Nouvelle Methode de classer les Hymenopteres ' of 1807. 

 In 1818, Gravenhorst and .Nees von Esenbeck drew up the first 

 satisfactory system of natural sequence, which was followed by 

 the former's ' Ichneumonologia Europsea.' Tliis work deals 

 exhaustively with the JchneumoxiDtE as understood to-day, to 

 the exclusion of all other Terebrant Hymenoptera, the characters 

 utilised for their subdivision being : a compressed or depressed 

 abdomen ; a petiolate or subsessile abdomen ; 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 ; upon these twelve genera and sixtj' subgenera 

 are based. The principal of the former were OpMon and Banclms, 

 which alone have the abdomen compressed ; Pimi^la and Xorides, 

 with the abdomen subsessile and the terebra exserted ; Tryplion 

 and Bassus, with the abdomen sessile, but the terebra concealed ; 

 6V?/2Ji«s, with petiolated abdomen and the terebra exserted; and 

 lastly, lehncnmon, with petiolated abdomen and concealed terebra. 

 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 JSchrauk, in 

 1781 — it would be quite impossible to refer here to the subtle and 

 gradual modifications which have since been found from time to 

 time to be needful, or to mention the many hundreds of genera 



