I06 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



5. The ninth tergum is complete in lower families, its widened 

 lateral parts being continuous dorsally at least in a narrow sclerotic 

 bridge, with which the proctiger may be united ; in the bees the ninth 

 tergum consists of two large lateral sclerites, known as the " quadrate 

 plates ", but the median part of the ninth dorsum is membranous and 

 not distinct from the proctiger. 



6. The second valvifers are oblong plates bearing anteriorly the 

 rami of the second valvulae, and posteriorly the third valvulae. Each 

 is articulated by its dorsal margin with the ventral posterior angle of 

 the first valvifer (not with the ninth tergum), and is provided with 

 the usual anterior and posterior muscles arising on the ninth tergum. 



7. The venter of the ninth segment is always membranous, there 

 being no intervalvular sclerites. 



8. The shaft of the ovipositor or sting is composed of the first 

 and second valvulae, the first being ventral, the second dorsal. The 

 second valvulae are united with each other beyond their convergent 

 rami, either solidly or by membrane, and two pairs of muscles are 

 inserted on their bases, one pair arising on the proximal parts of the 

 rami, the other on the inner faces of the second valvifers. These 

 muscles of the second valvulae are characteristic features in the 

 mechanism of the ovipositor or sting of the Hymenoptera, but they 

 appear to have no homologues in other insects. 



9. The third valvulae are free lobes ensheathing the distal part 

 of the shaft of the ovipositor; they vary greatly in length according 

 to the length of the ovipositor. 



10. The proctiger is always present. In lower families it consists 

 of a dorsal and a ventral plate, and bears a pair of small appendicular 

 processes ; in the higher families it becomes reduced to a simple mem- 

 branous tube or cone. 



Four examples, selected from the Tenthredinidae, Braconidae, Ich- 

 neumonidae, and Apidae, will serve to illustrate the characteristic 

 structure and some of the principal modifications of the ovipositor as 

 the organ is developed in the Hymenoptera. 



PTERONIDEA RIBESII (sCOPOLl) 



The relatively large abdomen of the female currant sawfly contains 

 the usual lo abdominal segments present in the Hymenoptera. The 

 eight pairs of spiracles are located in the lower parts of the tergal 

 plates. The first segment is broadly joined to the thorax; its tergum 

 is divided dorsally by a median membranous area, and the precostal 

 region forms a narrow postnotal plate of the metathorax ; the venter 

 of the first segment is reduced and contains no sternal sclerite. 



