12 INTKODTJCT10N. 



bearing distinctive sculpture. The second segment, near its base, 

 often bears deep sulciforni impressions at the sides, which are 

 known as the gastrocoeli, their apical margins being called the 

 thyridii. There are eight dorsal segments of which the pygidium 

 is "rarely visible, being retracted beneath the seventh segment. 

 There are also eight ventral segments in the male, but only six in 

 the female ; these are often longitudinally plicate, in the centre, 

 after death and this is owing to the contraction of the supple 

 tissues upon desiccation. The apical ventral segment is the 

 hypopygium and is of variable form and extent, often covering 

 the ba'se of the terebra, which is composed of the central true 

 ovipositor or spicula and its two lateral protecting valvulae or 

 sheaths. The length of the terebra varies in relation to the 

 concealed or exposed mode of life of the host-larva, being in some 

 cases twice as long as the insect itself, while in others it is barely 

 visible beyond the apex of the hypopygium. In the genus Khyssa, 

 which oviposits in sawfly grubs deeply buried in the solid wood of 

 trees, the terebra is strongly exserted, while in Ichneumon, which 

 lays its eggs upon the skin of exposed caterpillars, it is very 

 short. 



The legs, so distinctive in many groups of insects, are here 

 disappointingly uniform in structure, being nearly invariably long 

 and slender, with few modifications, though in the EXOCHIDES 

 they are short with the femora nearly globose. The basal joint 

 or coxa, however, often bears a little tuft of dense pilosity in the 

 ICIIXECMONIN^ known as the scopula ; it is sometimes dentate or 

 cristulate beneath, as in Phceogenes, and is always more or less 

 distinctly punctate. The next two joints compose the trochanter, 

 the apical joint of which is designated, when necessary, the 

 trochanterellus ; and this is closely followed by the elongate and 

 rarely dentate femur. The sometimes externally spinulose and 

 centrally intumesceut tibia is articulated to the end of the femur 

 and at its apex gives rise to spines or calcaria, which are usually 

 two in number, though sometimes there is only a single spine or 

 even none. The tarsus is always five- jointed, its apical claws or 

 onyches are sometimes internally pectinate or furnished with 

 comb-like bristles ; between the claws is the pad-like pulvilltis ; 

 and the basal joint of the front tarsi is excised beneath, forming 

 with the calcaria a beautiful apparatus for the cleansing of the 

 mouth and antennae. It should be borne in mind that the anterior 

 legs are the two front pairs collectively ; the posterior, the two 

 hind pairs collectively; and that the front and hind legs each 

 comprise but a single pair. 



The wings vary greatly in extent, though little in outline or in 

 the number of their nervures, and they do not extend beyond the 

 anus ; sometimes normally winged species are found with the wings 

 rudimentary, and in the females of Pezomachus these organs are 

 entirely wanting. The nervures, which are true veins in the 

 wings of ICHWEUMONID.E, at first sight appear so uniform through- 

 out the whole family that the older authors, with the exception of 

 \\ esmael, gained but few distinctive characters therefrom ; and 



