THE Hoa Louse 701 
the anterior border of the fourth segment, where they turn ventrad and 
slightly caudad, appearing as a blunt angle on the ventral wall; again 
passing laterad and caudad, they turn cephalad at the posterior border 
of the seventh abdominal segment and cross the ventral wall parallel 
to the posterior arm of the above-mentioned angle, turning caudad about 
the anterior border of the third segment. In the region of the fourth 
segment they unite to form the single ejaculatory duct, which crosses 
the mid-intestine parallel to the last loop of the vesicles and is easily 
recognized by its marked musculature. Near the anterior end of the 
basal plate the duct loses its thick muscular wall and becomes a thin- 
walled muscular tube which is twice folded upon itself and then passes 
along the median line dorsad of the basal plate through the wall of the 
vesica penis into the chitinous penis. 
_ A study of the copulatory apparatus of Haematopinus reveals a general 
resemblance to that of Pediculus and a much more detailed resemblance 
to that of the more closely related Linognathus limnotragi Cummings. 
The basal plate (Plate LVIII, 9, and Plate LXIV, 1, 2, and 3) lies within 
the ventral body wall and is much longer than broad, extending cephalad 
to. the anterior border of the sixth abdominal segment. Its proximal end is 
rounded; it appears to consist of two halves joined along a median suture, 
which indicates its probable double origin, according to Cummings, as two 
long apodemes. Its anterior edge is weakly chitinized. Then follows a 
region of strong chitinization for muscle attachment, where there are 
two small apodemes along the median line, one dorsal and one ventral. 
The median chitinization soon disappears, but the lateral continues as 
stout borders ending in knoblike enlargements with which the parameres 
articulate. In cross section the plate is seen to consist of two lamellae, 
a dorsal and a ventral, and anteriorly these are fused along their lateral 
borders. In the region just anterior to the articulation of the parameres 
the lamellae become slightly broader and the two surfaces separate from 
one another. The inner, or dorsal, lamella grows up and closely surrounds 
the dorsal wall of the vesica penis, and on its lateral regions the parameres 
develop as chitinous thickenings. The outer, or ventral, lamella grows 
up surrounding the whole copulatory apparatus, and at its dorsal lateral 
borders formsja deep fold on each side for muscle insertion (Plate LXIV, 
land 5). Such an outgrowth of the basal plate was not seen by Mjéberg, 
