204 ENTOMOLOGICAL SOCIETY 



socket joint (Fig. 5, d, /, and g). The spiculse branch near 

 the base of the sheath. The inner branches unite, forming a 

 loop, and the outer pass over the enlarged base of the sheath 

 and continue along the upper edge of the support and unite 

 with the triangular plate 9', which may be termed the spicule- 

 plate. The parts are shown somewhat separated at g, to better 

 indicate their relation. The spaces between the spiculae and 

 the support are enclosed by a membrane, which forms with 

 these parts a closed passage for the egg from the abdomen to 

 the ovipositor proper. 



It will be seen that what Westwood terms the base of the 

 support, which is, however, really its apex, and to which the 

 main piece of the ovipositor hinges, is free and does not origi 

 nate or attach to the yth ventral arc except by a loose mem 

 brane. In fact it is strongly attached only to the 8th dorsal arc, 

 and the two pieces, or plates composing it, are united at the 

 base, forming a true arc, homologous with and doubtless a modi 

 fication of a 9th dorsal arc, while the spicule-plate attaches to 

 the 8th dorsal arc and corresponds with the 8th ventral arc. 

 The spiculse are so intimately connected with the latter that 

 they would seem to appertain to the same arc of the 8th segment. 



The great size of the parts of the ovipositor in this species 

 make it an excellent example for study and enables one to trace 

 the parts without any difficulty. 



An examination of the figure of Pimpla conquisitor (Fig. 8) 

 reveals an exact correspondence in structure and relationship 

 of the parts, accompanied, however, with considerable modifi 

 cation in the size of the different pieces of the ovipositor and 

 supports. The comparatively much shorter basal plate (9) 

 greatly reduces the length of the outer branch of the spiculse 

 as compared with Metopius, and brings the spicule-plate (9') 

 almost to the apex of the supports. The sheaths are much 

 larger and their continuity with the support (9) is shown at d 

 and e. The manner of attachment of the superior channeled 

 piece of the ovipositor (10), shown enlarged at b and d, and of 

 the spiculse, together with the peculiar forking of the latter, is 

 found to be exactly similar to the same features in Metopius. 

 In Pimpla and most other species examined the inner branches 

 widen and become more or less thin and unicolorous with the 

 surrounding membrane with which they coalesce. 



A study of this organ in other Ichneumoids, including the 

 enormously developed organ of Thalessa, shows a practical 

 agreement in structure in all. 



The Chalcid ovipositor, while exhibiting considerable modifi 

 cations in the matter of supports and attachment of the superior 

 piece of the ovipositor and spiculse to the latter, is found to 

 agree in important particulars, as does also that of Cynips. 



