304 
Studies on Pedieulus 
The component parts of the apparatus. 
The copulatory apparatus of the male, when at rest, is usually 
completely retracted within the last three abdominal segments (Text- 
fig. 3). It issues through a large transverse slit upon the dorsal surface 
of the abdomen immediately behind the anus. The walls of this slit 
form the beginning of a flattened tube which is continuous with .the 
chitinous exoskeleton. At its deepest point of invagination into the 
body, the tube folds backward and inward like the partly inverted 
finger of a mitten, and its walls fuse distally \vith the chitinous structures 
of the evertible copulatory organs (see Text-fig. 3 where the pn.st-genita] 
[p. 5 ^./.] and pregenital fold, in front of p. pk, are shown). 
The essential farts of the apparatus are : (1) the basal plate, (2) the 
dilator (parameres), (3) the vesica penis, including its rib or strut, 
statumen penis, embedded in its wall, (4) the penis, and (5) the ductus 
ejacidatorius. 
(1) The basal plate (PI. Ill, figs. 1, 2 ; Text-figs. 1-4, B. P. or B. PI.) is 
of elongated form, concave dorsally in transverse section, and curving 
gently in a dorsal direction along its length. It measures 0-75-1-15 mm. 
in length depending upon the size of the male (the other structures 
below-mentioned vary correspondingly in size). The basal plate is 
greatly strengthened laterally by a rod-like thickening on each side 
which arises gradually and terminates distallv in a heavily chitinized 
rounded extremity. The pair of rounded ends articidate with the 
dilator which hinges upon them. Proximally the plate is bluntlv 
rounded, thin and almost colourless, slightly rugose near the margin 
for the insertion of muscles; signs of a median suture are usually dis¬ 
cernible. Distally, as is seen in sagittal sections (Text-fig. 3, B. PI. cl.), 
the basal plate splits into two lamellae which are in continuity with 
the chitin forming the post-genital fold (Text-fig. 3, p. g.f.). 
(2) The dilator 1,2 ', Text-figs. 1, 2, 4, Z)?T). Apart from 
lateral thickenings of the basal plate above described, the dilator con¬ 
stitutes the most heavily chitinized part of the whole apparatus. The 
structure is composite in origin for it is derived from two if not four 
chitinous rods (the parameres of Mjoberg) which through fusion of their 
distal extremities into a point have, functionally speaking, become a 
single V-shaped organ. The two rods diverge basally to their articula¬ 
tions on the basal plate. For purposes of description the name dilator 
is here preferred, it being more convenient to refer to the structure in 
the singular. The dilator measures 0-4-0-7 mm. in length. When the 
