NO. 8 INSECT ABDOMEN — SNODGRASS 87 



study of the egg-laying organ. The Central American species here 

 described, however, has a length of 20 millimeters, and the structure 

 of its ovipositor probably vv^ill be found typical of the family in 

 general. 



The abdomen of Amblydisca is cylindrical, and rigid except at 

 its attachments on the thorax. The first two segments are reduced 

 and their tergal plates are more or less united with each other and 

 with the third tergum. The postnotum of the metathorax is strongly 

 developed laterally, where its ventral ends are fused with the epimera. 

 but dorsally it is reduced to a narrow sclerotic bar beneath the over- 

 hanging posterior edge of the metathoracic scutellum. It is entirely 

 separated by membrane from the first abdominal tergum, except for 

 a small, flexible sclerotic bridge on each side, the two points of union 

 forming the fulcra on which the abdomen is movable on the thorax. 

 The sternal plates of the first two abdominal segments are narrow 

 and are concealed in a ventral depression at the base of the abdomen. 

 The distal part of the abdomen (fig. 28 A) is tapering, and ends with 

 the broad tips of the third valvulae (3VI) which normally ensheath 

 the end of the ovipositor (Ovp). 



The seventh segment of the abdomen is the first that is modified 

 in relation to the genital functions. Its tergum (fig. 28 A, VIIT) 

 resembles the tergal plates of the preceding segments, which have 

 prominent marginal paratergites (pt) with inflected ventral surfaces 

 containing the spiracles. The seventh sternum ( VIIS) is a triangular 

 sclerite with a free posterior margin, toothed at the apex, projecting 

 posteriorly as a subgenital plate beneath the base of the ovipositor. 

 Above the seventh sternum is a large vestibular cavity. 



The visible part of the eighth segment consists of a principal 

 tergal plate (fig. 28 A, VIIIT) exposed behind the seventh tergum, 

 and of a large, triangular paratergite on each side containing the 

 eighth spiracle (B, pt). The lower anterior angle of the paratergite 

 is connected with the dorsal posterior angle of the first valvifer 

 (B, iVlf) , which is normally concealed within the lower part of the 

 seventh segment by the invagination of the lower parts of the eighth 

 and ninth segments within the seventh (A). The intersegmental 

 membrane (B, Mb) between the seventh and eighth segments is re- 

 flected from the dorsal (anterior) margin of the second valvifer, 

 and ventrally is continued into the membranous floor of the vestibu- 

 lum over the seventh sternum. From the anterior wall of the vestibu- 

 lum there projects beneath the base of the ovipositor a small liplike 

 fold slightly thickened on its dorsal surface (B, VlllStn). This 

 fold is evidently a remnant of the eighth sternum. Above it there is 

 7 



