The Hog Louse 701 



the anterior border of the fourth segment, where they turn ventrad and 

 sHghtly 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 l:iecomes 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, 

 1 and 5). Such an outgrowth of the basal plate was not seen by Mjoberg, 



