The Hog Louse 685 



cuticula on either side of the mouth parts, below which they pass closer 

 to each other for a short distance before turning at right angles and passing 

 to the lateral walls of the head. At the anterior level of the " mandibles " 

 (Plate LXI, 2) the buccal plate is somewhat more tubelike, but it still 

 continues ventrad as a delicate cuticula alongside the mouth parts. This 

 prolongation appears now to be a continuation of the dorsal and ventral 

 surfaces of the plate, while in succeeding sections it comes to be a con- 

 tinuation of the dorsal ends of the pumping pharyngeal tube, the anterior 

 ends of which are now seen lying between the buccal plate and the dorsal 

 element of the piercers. In this anterior region a band of tissue crosses 

 the head transversely above the stomodaeum and appears to be attached 

 at either side to the lateral wall of the head just dorsad of the basal part 

 of the " mandibles " of Enderlein. It is very similar to epithelial tissue, 

 and each cell has a definite nucleus lying near its base. The cells attain 

 a considerable length, particularly on either side of the stomodaeum, and 

 their dorsal surface is attached to a well-defined basement membrane. 

 In sections stained with iron hematoxylin they closely resemble secreting 

 cells. At the level of the articulation of the basal part of the " mandibles " 

 of Enderlein with the triangular part, this band of tissue rests on the 

 top of the buccal plate, and at its most posterior part it appears to form 

 an attachment between the buccal plate and the lateral wall of the head. 

 The buccal plate gradually becomes flat and there is a marked increase in 

 the thickness and rigidity of the dorsal wall of the head. Also the shape 

 of the buccal cavity changes, marking the beginning of the ventral wall 

 of the diverticulum, but the mouth parts are still lying under the pumping 

 pharyngeal tube. As the chitinous intima of the buccal cavity passes 

 dorsad, it curves around into the lateral edges of the dorsal element of 

 the piercers, and at this point shows stronger chitinization, afterward 

 continuing as a fine cuticula to the ventral ends of the halves of the 

 pumping pharyngeal tube. The dorsal ends of these half tubes are also 

 continued as a fine cuticula, which passes downward to surround the 

 ventral part of the buccal cavity. Between these two chitinous layers 

 is a layer of epithelial tissue which broadens considerably on either side 

 of the mouth parts and there appears to contain some muscular elements 

 (Plate XLI, 3). Immediately behind the section shown in Plate XLI, 3, 

 the buccal plate divides into two arms united b}^ a thin cuticula which 

 forms the roof of the pumping pharynx and which, as it passes backward. 



