666 Laura Florence 



branch going to the disk must be the retractor muscle of the disk. 

 Osborn figured this large muscle lying in the tibia as inserted in the dorsal 

 wall of the tarsus, and a continuation passing from there to the dorsal 

 curve of the claw. He also figured a flexor muscle of the tarsus. Neither 

 of these two conditions has been found in the present investigation, and 

 the absence of flexor muscles of the tarsus and the claw may be explained 

 on the following grounds: the tarsus becomes defined as a segment distinct 

 from the tibia only after the final molt, and is then practically immovable, 

 while the claw in its normal resting position is bent over with its tip 

 touching the ventral anterior extension of the tibia, so that only an extensor 

 muscle is necessary for its function. No mechanism for ejecting the 

 protractile disk has been found, and, as Osborn suggested, this ejection 

 may be accomplished by means of an elastic framework. 



The foregoing account deals only with what may be called the skeletal 

 muscles of the louse. The muscles controlling the various systems of 

 the body are described later in their respective connections. 



The histological structure of the muscle is best seen in the material 

 fixed in Bouin's solution and stained with Mallory's anilin-blue connective- 

 tissue stain, when all the cross-striations stand out with great clearness. 

 All the muscles have a well-developed sarcolemma and are richly supplied 

 with peripheral nuclei. 



THE VASCULAR SYSTEM 



In the writings of the early investigators of the Pediculidae, no real 

 description of the dorsal vessel is to be found. Landois (1864:11), after 

 many attempts, distinguished in freshly molted insects a slender tube 

 originating in the region of the transverse tracheal band. He traced it 

 cephalad to the middle of the abdomen, but could follow it no fai'ther. 

 Its pulsations were more rapid than those of the stomach. IMjoberg 

 (1910:22.3) pointed out the similarity of the heart in the two groups 

 which he studied, and drew attention to the lack of any thorough work 

 in the Siphunculata (Anoplura). According to Schroder (1912-13:390), 

 Provazek in 1905 described and figured the heart of Hacmatopinus 

 spinulosus Burm., and this appears to be the first anatomical description 

 of the heart of a siphunculatan. Miiller (1915:27) has figured the heart 

 of the clothes louse in gross and in sections, and has described in detail 

 its anatomy and its pulsations in living specimens. Harrison (1916 b:220) 



