SEXUAL CHARACTERISTICS OF THELIA 579 
cephalad within the abdomen half-way through the eighth 
somite. To this internal portion muscles are attached which 
move these appendages. The oedagus is a heavily chitinized, 
tubular organ containing the penis. Its proximal end articulates 
with the caudal tip of the ninth sternum. The oedagus bends 
sharply dorsad and comes into close approximation with the 
anal tube (figs. 24 and 25, oe.). 
The female external genitalia are seen in figures 28 and 29. 
The appendages of the eighth segment are two sharply pointed 
plates, each articulating with the lateral remnant of the eighth 
sternum (fig, 28, gn. 8). They form a strong, closely fitting 
sheath about the ovipositor, being interlocked along the median 
plane by a sort of dove-tail union. The anterior appendages of 
the ninth segment form a tube, the ovipositor, open along its 
ventral border at both its proximal and distal ends (fig. 28, gn. 9). 
Its proximal portion consists of two strong, chitinous rods which 
diverge and articulate laterad with the two small sclerites repre- 
senting the ninth sternum. The distal third of the ovipositor 
bears three pairs of well-defined teeth along its dorsal border. 
The third pair of gonapophyses, the posterior pair of the ninth 
segment, are flattened sclerites, laterally placed, partly covering 
the ovipositor and its sheath (fig. 28, gn. 9’). Each articulates 
with the caudal portion of the ninth sternum of its respective 
side. 
In parasitized males the oedagus and claspers are greatly 
reduced in size and are located on the ventral portion of the 
enlarged eighth somite (figs. 26 and 27). The oedagus is short- 
ened to form a stout tube, and the claspers do not reach even to 
the base of the ninth segment, but retain quite well their orig- 
inal form. The ventral valves show much less reduction in 
size than the oedagus or clasper. They, however, present many 
irregularities in that the free caudal projections aze often mis- 
shapen and of unequal length. On the average, the ventral 
valves are reduced only 12 per cent and the maximum reduction 
found was 24 per cent of the normal length. Their reduction is 
not as constant as that of the other male genital appendages, for 
in males, otherwise greatly altered, they may at times be prac- 
tically normal in length (fig. 26, v.). 
JOURNAL OF MORPHOLOGY, VOL, 32, NO. 3 
