14 BULLETIN 45, UNITED STATES NATIONAL MUSEUM. 



attaoliineiit to tbe metatliorax, tlie teniiMi sessile, subse-ssile, or petiolate 

 ex'^iressing the form of attaebmeut. It is, however, iievei- attached to 

 tbe (lorsuui of the metauotum, as in the Evauiidie and some Bracou- 

 ida^ 



In connting the abdominal segments, the basal one is usually referred 

 to as the lirst segment or the petiole; sometimes, however, this seg- 

 ment is so short as to be invisible from above, or at least not visiblf; 

 until the abdomen has been detached from the metatliorax; it is then 

 usual to designate the second as the tirst. 



Tbe 3hai)e of the abdomen is generally ovate, ovate-conic, or oval, 

 but often oblong-oval, broadly oval, fusiiorm, or linear. It is rarely 

 greatly compressed, although frequently depressed or somewhat tlat- 

 tened. 



In some genera, in the Platygasterina> and Scelionina', the females 

 are furnished with a peculiar horn like structure at the base of the 

 abdomen that projects forward over the metathorax, and, indeed, often 

 as far forward as the head (PI. xi. Fig, 0). It gives to these insects a 

 singular appearance, but otherwise has no functional significance, 

 being merely a sexual peculiarity. 



The abdomen reaches its gi eatest length in proportion to the rest of 

 tbe body, probably in the genus Macrotclcia (PI. ix. Fig. G), and its 

 most unique shape in Suetognstei' (PI. xii, Fig. 4). 



Connected with the abdomen are the important organs of reproduc- 

 tion, tbe ovipositor, etc., which will now be described. 



THK OVIPOSITOU. 



In tbe difterentiation of its parts, the ovipositor, in this family, 

 agrees with other terebrant Hymenoptera, the only visible difference 

 being that in the whole group, excei)t in three or four abnormal indi- 

 viduals, tbe outer sheaths are conjoined and form a tube or scabbard 

 at tbe tip of tbe abdomen that affords ])rotection for the ovipositor 

 proper and its two spicuhe when not in use. Distinct sutures are 

 visible in this tube, and after death it can be readily separated into 

 two plates. 



This tubular formation of the sheaths reaches its highest develop- 

 ment in the genus Proctotrypes. 



On PI. I two forms are shown. Fig. G represents that of Froctotrypes 

 caudatm Say, our largest species. Here the tube is as long as the 

 abdomen, slightly compressed and curving downward at tip. It is 

 readily detached, and in the tigure is represented partly detached, in 

 order to show tbe internal structure of the ovipositor. The terebra, or 

 oviiwsitor proper (f6a), is the piece through which the egg passes; it is 

 composed of three pieces, a broad upper plate and two spicula? [spc) 

 or lower plates, tbe latter united to the former by a dovetailed joint 

 (see Fig. 0, A and B). These three pieces are dilated and lobed at 

 base («p/), and are conne* '^ed by strong muscles to a basal plate [bp) 



