16 THE entomologist's recoed. 



instifiator, and Marsham (1797) had read a learned paper before the 

 Linnean Society upon the economy of IcJuteioiunt. vianifestatijr : a few 

 isolated species had, besides, been described by Albin (1720), Eay (1710), 

 and Forster (1771). 



The century had, however, hardly set in before progress became 

 marked ; in 1802, Schrank's Fauna Boica, and, in 1803, Latreille's 

 Dictionnaire greatly assisted Fabricius in the first ichneumon book, 

 Sijstema Fiezatonnn (1804). Many works bearing more or less upon 

 the subject were published upon the continent during the following 

 years for which we have here no space, nor is it necessary to individu- 

 ally notice them since such knowledge of these insects, as at that time 

 existed, is excellently summed up in Gravenhorst's three thick volumes 

 of the Iclmeumunohxiia Juirojjaea in 1827, an account of whose system 

 had already been published in his Compectus Ichneumonidum (1818). 

 The later work constitutes the foundation of all subsequent discoveries, 

 and it is only within quite the last few years we have dared to depart 

 from the mode of classification therein laid down to any appreciable 

 extent. 



The peculiar difficulty experienced by the student of these parasites 

 is the extreme similarity in structure of specimens which are obviously 

 specifically distinct ; and hence Gravenhorst resorted in a great measure 

 to the always unsatisfactory guide of colour for his differences ; indeed 

 such structural points as exist are so minute as to be quite worthless to 

 an early writer who could not, of course, possibly rely, for lack of 

 observations, upon their constancy. In truth, the subject appears to 

 be fraught with so many obstacles that, until the present decade no 

 second comprehensive work upon the group has been attempted, but 

 more or less complete monographs have, from time to time, appeared 

 in various countries. The first of these worthy of note is Wesmael's 

 fine contribution to the X(nit\ Mem. Ac. Bruxiiles, of a synopsis of 

 Gravenhorst's first subfamily, the Ichneumonidae [seni^H stricto), which 

 is here subdivided and tabulated by a master hand. To this the author 

 issued seven valuable supplements during the following fifteen years 

 and, in 1849, a capital method, with many descriptions, of classifying 

 Jurine's genus Ammalon, in Gravenhorst's third family. Where 

 Wesmael had left the subject it was taken up by Holmgren, who not 

 only completed and collected it, but considerably augmented it in his 

 three vols, of Ichneumonoloijia Succica (1864-71-89). Gravenhorst had 

 divided the whole group into five great families — the Ichnciononidae 

 (treated of by Wesmael), the Cry})tidae, OpJiionidae, Tri/pJicmidae and 

 Piniplidae. Of the last three, Holmgren very greatly assisted in the 

 comprehensive classification in his Swedish 3/o»o//raj)/;/rtf', in the- Sr. 

 Ak. Handliniiar, in 1858, 1859, and 1860 respectively ; besides more 

 detailed BhpoRit'ioncsoi Gravenhorst's genera A'.c(W(i(s (1873), (.'anipoplex 

 (1872), and Mewleptim, partim (1876). 



We must next turn momentarily to the numerous works of Forster, 

 which both entangled and untangled this difficult subject. His 

 Monoipaphie dcr Gattinifi Pczoiiiachiis (1850-51) is a rule of thumb, by 

 which to distinguish the extremely closely allied species of one of 

 Gravenhorst's genera of the second family ; in this, however, the 

 former is very difficult to follow satisfactoril}', many of his species are 

 mere colour varieties, and his main (costal) division has since been 

 relinquished. There followed equally important and more satisfactory 



