The Hog Louoe 703 



line with their basal articulations. Here the chitinous structure is no 

 longer a canal, but two divergent arms which may cor-respond to the 

 statumen penis of Nuttall. 



^Vlien killing lice with chloroform it was noticed that the males frequently 

 ejected the copulatory apparatus in part or completel}^ and this character- 

 istic has been utilized in the study of the musculature and movements 

 of the apparatus. The protractor muscles of the basal plate have their 

 origin in the ventral wall of the ninth abdominal segment where it turns 

 dorsad, and their insertion in the anterior ventral surface of the basal 

 plate. They form a thin plate of muscle fibers Ijnng parallel to one another 

 and identical in outline with the plate. When they contract, the basal 

 plate is drawn caudad until the proximal edge lies just anterior to the 

 boundary between segments 6 and 7, and the parameres are protruded 

 from the sexual orifice for from one-third to one-half their length. Their 

 dorsal aspect shows no collar-like membrane forming a sheath for the 

 transit of the vesica penis as figured by Nuttall in Pediculus. Its place 

 is taken by the already described upgrowth of the basal plate. They point 

 dorsad and slightly cephalad, so that their ventral aspect is now caudad 

 (Plate LXIV, 4). They are controlled by muscles which lie at rest along- 

 side them and which, by their contraction along with or immediately 

 following that of the muscles of the basal plate, hold them rigid during 

 copulation. There are ten muscle strands on either side, of which the 

 five posterior lie in a regular succession and the five anterior in a close 

 group. They originate in the ventral l)ody wall in the region of segments 

 6, 7, and 8. The posterior strands are inserted in the deep lateral fold 

 of the upgrown ventral lamella of the basal plate (Plate LXIV, 5), and 

 the anterior strands are inserted as a stout tendon in the anterior dorsal 

 border of this upgrowth. Mjobcrg (1910:189) has explained the purpose 

 of the genital plate, at any rate in some cases, as the basis of attachment 

 of these muscles, and his figure of Hae77iatopinus btifali de Geer shows 

 them inserted in the border of the genital plate. C'ross sections through 

 this region in the hog louse show these muscles originating latcrad of the 

 genital plate. The dorsQ,-ventral lateral muscles of the abdomen next 

 contract and drive the coelomic fluid caudad and into the vesica penis, 

 which is thereby everted carrying the ejaculatory duct and the penis 

 along with it. The thick muscular part of the duct has been drawn 

 caudatl until its posterior end lie 5 at the level of the articulation of the 



