12 Rev. T. A. Marshall's Monograph of 



ing a support to the terebra ; this last briefly exserted, its 

 valves broad, compressed, of variable form. 



The parasitic habits of these insects, difiering from those 

 of the majority of the Braconidse, have been known ever 

 since the year 1695, the date of the " Arcana Naturse " of 

 Van Leeuwenhoek, who first observed them attacking 

 Aphides. His observations have been repeated and ex- 

 tended by a number of subsequent writers, so that the 

 principal facts must be familiar to all entomologists. It 

 is therefore unnecessary here to enter into many details. 

 There is nothing remarkable in the process of oviposition, 

 which is conducted in the manner usual with parasitic 

 Hymenoptera : the female confides to each puceron a 

 single egg, which is matured in a few days ; the larva 

 remains generally in the body of the victim till the final 

 change, making no separate cocoon ; the interior of the 

 inflated Aphis is however lined with very fine silk. This 

 is the general rule, to which the genus Praon, so far as is 

 known, offers the only exception, to be mentioned here- 

 after in its place. The apterous adult Aphides are gener- 

 ally chosen by preference, probably because they are 

 commonly of large size, and supply a greater portion of 

 nutriment. 



No doubt a vast number of these destructive vermin 

 perish annually from the attacks of their enemies, but it 

 does not appear that the mischief they cause is ever 

 effectually controlled. The amateurs of rose-culture 

 generally find that an infested plant shews strong signs of 

 deterioration in spite of the industry of the female Aphi- 

 dius, which, to be eft'ectual, must be supplemented by the 

 more vigorous measures of human skill. Some of these 

 parasites, as the common Aphidms avenm and A. ervi, 

 Haliday, are known to attack several different kinds of 

 Aphis ; but in general they are more exclusive, attaching 

 themselves each to one particular species. 



The number of species is certainly very large, but so 

 little attention has been paid to their distinctions, that it 

 is impossible to speak with any confidence ; the subject 

 may almost be regarded as untouched. In fact there exist 

 only two monographs to which recourse may be had for 

 detailed information, that of Nees v. Esenbeck, containing 

 15 species, and that of Haliday, which extends to 44 : 

 the few scattered descriptions occurring in other authors 



