122 PIMPLINE ICHNEUMONIDAE 



notum and pleura become fused with the sternum for a greater 

 or lesser distance. The amount of this fusion is used in classi- 

 fication to species, and the presence or absence of it is made use 

 of for generic distinction. The sternum is divided into an anterior 

 and a posterior portion by a transverse groove. The latter 

 portion is again divided into two parts by a longitudinal mid- 

 ventral groove. 



Considerable variation from the typical form in regard to the 

 construction of the sternal plate has been found. A large part, 

 often as much as half of the posterior portions of this plate may 

 be membranous in place of being mainly composed of chitin, 

 as is the case in some species. It is impossible to determine 

 whether this characteristic is the primitive condition or is a 

 degeneration, though the weight of evidence would point towards 

 the latter, as the few species possessing this modification are in 

 other respects the most highly developed of this group. 



The third segment, like the second, is truncate at its apex, 

 while the fourth, fifth and sixth segments are prolonged laterally 

 at the apex. There is a gradual increase in size in these segments, 

 otherwise their structures closely resemble each other. In each, 

 the notum and pleura are fused, but the sternum is a separate 

 plate. On the pleura are laterally impressed lines converging 

 toward the base. The sternal plates of these segments are 

 separated by a mid-ventral longitudinal groove. On eithej* side 

 of this groove is a small projection, the tips of which point toward 

 each other. The size and position of these projections vary in 

 different genera. This character is used for generic classification. 



In the female the last three segments of the abdomen are 

 highly specialized. Ventrally they are plow-share shaped. 

 The seventh is the deepest segment of the abdomen. Its ventral 

 plate, however, is very small. Between the dorsal portions of 

 the seventh and eighth segments is the membrane used by the 

 female for coiling up the ovipositor, before thrusting it into the 

 tree in which she desires to oviposit. The ovipositor becomes 

 external on the ventral side between the seventh and eighth 

 segments. It is long and slender, varying in length; in some 

 species attaining a length of five or six inches and is always 

 longer than the body of the insect. It is composed of three 

 lateral sections which interlock. The ventral plates of the eighth 



