358 W. D. FUNKHOUSER 



for want of a better name, the lateral valves. These are sometimes folded 

 inward to meet each other, and sometimes they project directly caudad 

 leaving the lower surface of the anal tube exposed. When the latter 

 condition obtains, or when the lateral valves have been dissected away, 

 the ventral part of the rectum is seen to consist of a somewhat chitinized 

 plate which is probably the vestigial sternum of the tenth segment. The 

 area below the rectum and cephalad of the valves is occupied by the inter- 

 segmental membrane. From the region between and at the base of the 

 valves arises the oedagus. This structure is heavy and curved (Plate 

 XXXIX, 3), extending first caudo-dorsad, then dorsad, and then dorso- 

 cephalad. Near the base of the oedagus arises a pair of styles, or forceps, 

 which usually extend outward laterally and are subject to great modifi- 

 cation in shape. The sternal plate, which is apparently the sternum 

 of the ninth segment, bends almost directly upward at its tip and in some 

 species extends so far dorsad as to form a posterior wall behind the oedagus 

 (Plate XXXIX, 3). The oedagus contains the penis, a long, white, fila- 

 mentous tube which is seen only on dissection. 



The variation in position and structure of the parts of the genital 

 apparatus is considerable (Plate xxxix, 4-28), and it is this variation 

 that suggests their taxonomic importance. So far as has been studied 

 such variation is largely generic, and the figures have been purposely 

 drawn from a rather wide range of genera. From their position the 

 various plates seem to be only modifications of normal sclerites of the 

 abdominal segments, but this assumption may prove incorrect if 

 embryological evidence is obtained. In fact the paired condition of 

 most of the plates — even the sternal plate, which superficially^ appears 

 to be merely the extension of the ninth sternum — would suggest the 

 possibility that these structures are true appendages, homologous with 

 the very generalized developments on the abdomens of such low forms 

 as certain Thysanura. 



The terga of the ninth, tenth, and eleventh segments are usually visible 

 in the male. In some cases the tenth and the eleventh are hidden within 

 the ninth (Plate xxxix, 5) and in some cases they are projected (Plate 

 xxxix, 14); but in all cases they cover the anal tube and form a dorsal 

 roof over the rectum. The ninth tergum is the only one suitable for 

 taxonomic use, and this is usually best seen from a lateral view. P'rom 

 this aspect the sclerite appears as a subtriangular piece (Plate xxxix, 5) 



