The Hog Louse 689 



m a common duct for a short distance before entering the middle of the 

 dorsal surface of the piercer sheath by a common opening, while in 

 Haemato-pinus eurysternus she describes them as running separately to 

 the opening into the salivary duct of the mouth parts. Peacock (1918: 

 115) refers briefly to Martin, and to a dissection made by Mr. Lloyd, 

 Chief Entomologist to N. Rhodesia, as demonstrating that the four 

 salivary ducts open into the bulbous structure at the posterior end of 

 the chitinous salivary tube. 



Of these interpretations that of Sikora is probably the most accurate, 

 because it alone describes an arrangement of the ducts which allows of 

 their being drawn forward by the mouth parts during feeding without 

 danger of their rupture. 



Pat ton and Cragg (1913:5.59) describe a small collection of round cells 

 surrounding the esophagus and constant in position, which differ from 

 the cells of the fat body in their more glistening appearance. They dis- 

 tinguished no duct with certainty, though in some dissections a fine filament, 

 which may have been a duct, was seen passing upward with the salivary 

 duct. Miiller (1915) discusses these cells in connection with the fat 

 body, but remarks that up to that time no fat has been demonstrated in 

 them. Harrison (1916 b: 220) says that in the Siphunculata (Anoplura), 

 groups of specialized binucleate cells, richly tracheal ed, lie about the 

 ducts of the salivary glands, at the base of the esophagus. Sikora (1916: 

 57-58) gives a detailed account of the structure and appearance of these 

 cells, which she calls " grosszellige Drtisen," in Pediculus vestimenti, 

 and mentions their presence in the other species investigated. She 

 considers them as quite distinct from the fat cells and suggests that they 

 withdraw some constituent from the body fluid and store it or act on it 

 in some way before returning it to the body fluid. 



In the hog louse there is a cluster of small, subcircular cells, arranged 

 like a pair of wings, lying above the base of the esophagus. Between 

 these cells and the esophagus pass cephalad the dorsal vessel and the 

 ducts of the salivary glands. On dissection each half of the cluster is 

 found to consist, on the average, of forty small cells united by a network 

 of very fine tracheoles. The two median posterior cells, which are some- 

 what larger than the others and pear-shaped, lie side by side on the end 

 of the esophagus with their pointed ends caudad', and from each of them 

 a slender tracheolc passes to the surrounding network of the fat cells 



