THE Hoc 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 lymg 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 by a thin cuticula which 
forms the roof of the pumping pharynx and which, as it passes backward, 
