The Hog Louse ' 655 



the thorax. These were described in this and other Siphunculata 

 (Anoplura) by Endcrlein (1904:126), who named them " Hinterhauptvor- 

 satz " and thought that morphologically they probably originated as 

 tendons of the retractor muscles of the head. Mjoberg (1910:202-203) 

 named them the " occipital apodeme." Gross dissection reveals the 

 continuation of these processes as muscle bands having their origin on 

 the apodeme of the metathorax, while muscles controlling the lateral 

 movements of the head are inserted on their posterior lateral borders. 



The dorsal surface of the thorax is strongly chitinized and the segments 

 are completely fused with one another. In mature lice the sternal plate 

 is present on the ventral surface. On the prothorax, and also on the 

 anterior angles of the sternal plate, is a pair of very small openings 

 approximately 0.03 millimeter in diameter, which are present at all stages 

 of development (Plate LVIII, 6, 8, and 10) and have been passed over 

 or variously described up to the present time. Stevenson (1905:15), 

 in his description of the thorax, says: " On the ventral surface between 

 the appendages is a chitinous shield. In each anterior lateral angle of 

 this shield or plate is an opening called the osteole, leading from a canal 

 that extends cephalad." ]Mj6berg does not mention either of the pairs 

 of openings, and Neumann (1911:407) describes "a pair of verjr small 

 thoracic stigmata "^ and " a small stigma in each anterior angle "^ of 

 the sternal plate. Patton and Cragg (1913:548) describe both pairs of 

 openings as stigmata. On the sternal plates of seventeen species of 

 Siphunculata (Anoplura) figured by Kellogg and Ferris (1915: PI. IV), no 

 such openings are present. 



Gross dissection has shown that these openings are quite different from 

 the stigmata of the tracheae, are without a closing device, and communi- 

 cate with a canal which has no connection with the respirator3^ system. 

 The dorsal openings on the prothorax are connected with those on the 

 sternal plate by a rigid, uniformly chitinous canal passing directh^ dorso- 

 ventral laterad of the thoracic tracheal trunk. One short branch is given 

 of? almost at right angles to the main stem and at about one-third of the 

 total length of the latter from its dorsal surface, and passes caudad 

 terminating in the transverse band of muscle which lies between the second 

 pair of legs (Plate LVIII, 12). Series of cross sections made through the 



^ Translated fro.'J the original French. 



