708 LavuRA FLORENCE 
whose anterior border lies approximately on the anterior border of the 
fourth segment. . | 
The structure of the female copulatory apparatus is much simpler than 
that of the male. It is situated in the last three segments of the body, 
and the external indications of sex are the shape of the abdomen, two 
triangular chitinous plates on the dorsal surface of segment 9 (which 
ends in two pointed lobes), and the gonopods on the ventral surface of 
segment 8. The gonopods (Plate LVIII, 11) are flat processes, triangular 
in shape. Their median free border is somewhat strongly chitinized 
and is set with a row of stout hairs. Anteriorly they are joined by a 
fold of the integument which projects caudad in two blunt points. As 
has already been said, they appear to have arisen as an infolding of the 
integument of the segment. The sexual orifice is on segment 8 under 
'. the anterior border of the gonopods. It leads directly into the vagina, 
a thin-walled chitinous sac lying close to the ventral body wall and at 
its anterior end passing into the uterus ventrad of its semicircular coil. 
In Pediculus the walls of the vagina are covered with minute, outward- 
pointing teeth. In Haematopinus no teeth could be seen on the vaginal 
wall in gross preparations treated with potash and mounted in balsam. 
A plate of closely set muscle fibers originates in the anterior border of 
segment 7 immediately posterior to the ventral abdominal muscle plate, 
and is inserted in the anterior border of the gonopods. The contraction 
of these muscles raises the gonopods and brings the sexual orifice and the 
vagina into position for copulation. Muscle fibers originating in the 
lateral wall of the vagina and in that of the uterus near its passage into 
the vagina, are inserted in the sternite of segment 9, and by their contraction 
draw the vagina and the uterus to their resting position. 
The histological structure of the ovarian tubes at different stages of 
development has been thoroughly studied and described by Gross (1906: 
352-364), and a brief résumé of his work is here inserted. There is no 
peritoneal wall surrounding the egg tubes, and the tunica propria (base- 
ment membrane) is unusually well developed. In the terminal threads 
of adult females the content consists of a homogeneous granular proto- 
plasm which Gross regards as degenerated remains of the cells to be found 
in younger stages. Landois (1864:16) had seen these cells also in the 
terminal chamber of Phthirius, and he considered them as specific yolk- 
forming elements and hence the terminal chamber of the one-egg tube 
