The Hog Louse 663 



and presternum. It lies just anterior to the stomach, below the esophagus, 

 and is covered ventrally by the thoracic ganglia and many fat cells. The 

 posterior band consists of two strands and passes across the ventral 

 surface of the stomach. From each of the points of its insertion in the 

 coxae of the third pair of legs, a muscle passes somewhat obliquely cephalad, 

 and these muscles are inserted in the posterior arms of the apodeme 

 where they enter the anterior transverse muscle band. In sections made 

 through lice having the stomach filled with blood, the transverse muscle 

 bands appear to be imbedded in the stomach, owing to its walls having 

 become distended on either side of them. 



The work of Landois and of Mtiller has made known the great difference 

 in the longitudinal abdominal musculature of the two sexes of the man- 

 infesting louse, and Nut tall (1917 a: 296) has summarized this difference 

 as follows: 



Dorsal abdominal Ventral abdominal 



muscles are present muscles are present 



under segments under segments 



In the male 2, 3, 4, 5, 6, 7, 8 2 + 3, 4, 5, 6 



In the female 6, 7, 8 2, 3, 5,6 



In the hog louse no such difference is found. In both sexes a dorsal 

 muscle extending the whole length of the abdomen is present. It consists 

 of some eight muscle strands on either side of the median line. In segment 

 1 these strands converge to the point of their attachment to the posterior 

 surface of the metathoracic apodeme, and posteriorly, in segments 8 and 

 9, the two halves of the plate diverge and the heart lies between them. 

 The contraction of the muscle plate raises the posterior end of the abdomen. 

 In both sexes the ventral muscle plate (Plate LIX, 4) begins in the anterior 

 border of segment 2 and extends caudad to the posterior border of segment 

 6. The number of strands in each segment is apparently not arbitrary, 

 and the following have been found most frequently: 



Number of strands Number of strands 



in male in female 



Segment 2, 12 central and 4 lateral 10 central and 4 lateral 



Segment 3, 14 . 18 



Segment 4, 14 16 



Segment 5, 14 . 16 



Segment 6, 14 16 



