492 HYMENOPTERA 



suitable term for this part, which is of great importance in 

 systematic entomology, owing to the extreme variety of characters 

 it affords. Although it is clear that the propodeum is, in large 

 part, an abdominal segment, yet its morphology is still uncertain ; 

 what parts are pleural, what tergal, and what may be chitinised 

 spiracular area, or portions of the metathorax, being undetermined. 

 The ventral portion of the propodeum affords a strong contrast 

 to the dorsal part, being so small that it has frequently been 

 described as absent ; it is, however, not difficult to detect it in 

 the position shown at d, Fig. 333, B. 



Although the true first segment of the abdomen is detached from 

 its normal position and added to the thorax, yet the term abdomen 



is conventionally restricted to the part 

 that commences with the true second 

 segment, which, in counting the number 

 of abdominal segments, is reckoned as 

 being the first. There are two modes 

 of articulation of the Hymenopterous 

 abdomen with the alitrunk ; in one 

 (Fig. 336, A) the base of the abdomen 

 remains of the calibre usual in Insects, 

 while in the other (Fig. 336, B) it is 

 FIG. 336. Articulation of abdo- greatly contracted, so that the two 



men and alitrunk of, A, Cim- 



bex, B, Vespa. a, Propodeum parts are connected only by a slender 



or median segment ; 6 dorsal gtalk the pe tiole. The petiole, besides 

 plate oi first (second true) ... 



abdominal segment or petiole ; articulating in a very perfect manner 



e spiracle of the propodeum ; M th p ropodeum by me ans of cer- 

 a, hind coxa ; e, ventral plate J 



of first (second true) abdorni- tain prominences and notches, is also 

 connected therewith by means of a 



slender ligament placed on its dorsal aspect and called the 

 funiculus, shown in Fig. 333, A, just at the extremity of the 

 pointing line k. This mode of articulation gives great freedom 

 of motion, so that in some Petiolata (Ampulex^) the abdomen can 

 be doubled under the body and the sting brought to the head. 

 It is worthy of note that even in the Sessiliventres as the sub- 

 Order with broad-based abdomen is called some amount of 

 movement exists at the corresponding spot ; while, as shown in 

 Fig. 336, A, between a and b, there exists an exposed membrane, 

 the homologue of the funiculus. 



The number of abdominal segments that can be seen in the 



