30 



William T. M. Forbes 



the socius, which is conspicuous in the Thyatiridas and the Hemitheinae. 

 The ventral part of the segment, when it appears at all, forms a plate 

 between the anal tube and the penis, known as the transatilla, in many 

 cases articulated with the base of the valves. 



The end of the intestine is commonly a long tube, in many species 

 strengthened by the scaphium above and the subscaphium below. 

 Whether these structures represent the eleventh segment is an open 

 question. They may be simple bands or plates, or they may bear spines 

 or be of striking forms. The gnathos is a partially free subscaphium 

 articulating directly with the uncus. 



Fig. 22. typical female genitalia 

 (leucania pallens). 



In most females the abdomen has 

 seven visible segments (fig. 22). The 

 eighth and ninth segments are retracted 

 within the seventh and are, for the 

 major part, composed of membrane. On 

 the ventral surface of the eighth seg- 

 ment is the vagina, with a chitinous 

 plate below it. The remainder of the 

 segment is, in most cases, a short cylin- 

 der. The ninth segment is divided into 

 two lobes between which lie the anus 

 and the opening of the oviduct. The 



Fig. 23. head of laeva with 

 set.e numbered by dyar's sys- 

 TEM (RIGHT) AND heinrich's 

 SYSTEM' (LEFT) 



Ad 1; Ad 2 , Ad 3 , Anterodorsal setae 

 of epicranium; adf 1; adf 2 , adf ren- 

 tal setae; Ant, antenna; CI, cly- 

 peus; Ep, epicranium; Ft, front; 

 F 1} its seta; L 1; lateral seta of 

 epicranium; Lm, labrum; md, 

 mandible; 3 , 2 , 3 , ocellar setae 

 of epicranium; Pd^ Pd 2 , postero- 

 dorsal setae of epicranium; So^ 

 So 2 , So 3 , subocellar setae of epi- 

 cranium 



usual condition is shown in figure 22. 



The four most primitive families show a different structure. In 

 the case of the Micropterygidse there are eight fully developed seg- 

 ments, and the ninth and tenth are invaginated within the eighth, the 

 tenth segment being fairly well developed (fig. 34). The Eriocraniidse 

 and the Incurvariidse have a complex piercing ovipositor, whose struc- 



