14 BULLETIN 45, UNITED STATES NATIONAL MUSEUM. 



attachment to the metatborax, the terms sessile, subsessile, or petiolate 

 expressing the form of attachment. It is, however, never attached to 

 the dorsum of the metauotum, as in the Evauiidte and some Bracou- 

 idte. 



In counting- the abdominal segments, the basal one is usually referred 

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

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

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

 usual to designate the second as the first. 



The shape of the abdomen is generally ovate, ovate-conic, or oval, 

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

 greatly compressed, although fre<piently depressed or somewhat Hat- 

 ten ed. 



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 metatliorax, and, indeed, often 

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

 singular appearance, but otherwise has no functional significance, 

 being merely a sexual peculiarity. 



The abdomen reaches its gieatest length in proportion to the rest of 

 the body, probably in the genus Macroteleia (PL ix. Fig. 6), and its 

 most unique shape in Sactofjastcr (PI. xii. Fig. 4). 



Connected with the abdomen ar(^ the important organs of reproduc- 

 tion, the ovipositor, etc., Avhich Avill now be described. 



THK OVII'OSITOU. 



In the differentiation of its p;irts, the ovipositor, in this family, 

 agrees with other terebrant Hymenoptera, the only visible difference 

 being that in the whole group, except in three or four abnormal indi- 

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

 at the tij) of the abdomen that a&brds protection for the ovipositor 

 proper and its two spieuhe 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 Proctotrypcs. 



On PI. I two forms are shown. Fig, G represents that of Froctoinji)cs 

 caudatuH 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 figure is represented partly detached, in 

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

 ovipositor proper {tha)^ is the piece through which the eg'^ passes; it is 

 composed of three i)ieces, a broad upper plate and two spieuhe (.s^jo) 

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

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

 base (.vpO? '"^^^^ ''^^'^ counet^^ed by strong muscles to a basal plate {hj)) 



