156 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
phageal valve, and at the point where the stomach and ileo-colon 
come together. 
According to Dimmock (’ 81 ) both labrum and hypopharynx take 
part in the formation of the proboscis canal, the latter stylet form¬ 
ing the floor. Ivrapelin (' 82 ) on the other hand, considers that 
this canal is wholly labral in origin. It w r as not possible to 
decide between these views. The shelf formed by the produced 
lower internal angles of the labrum (pi. 16, fig. 46-47) favors Krape- 
lin’s view, but in this case the delicate character of these plates 
would seem to require that the hypopharynx should be drawn up 
against them during blood sucking and so indirectly complete the 
proboscis canal ventrally. 
Since the anterior wall of the clypeus is forward of the bases of 
the moutliparts generally, the labrum meets the head some distance 
in front of the point where the mandibles, maxillae, hypopharynx, 
and labium are inserted. In this region the section of the proboscis 
canal is that of an arch, and the hypopharynx unquestionably sup¬ 
plies the flattened floor (pi. 13, fig. 3). Caudad of the bases of the 
mouthparts (pi. 13, fig. 4) the canal may be considered as intra- 
cephalic and as pharynx. At this point the thick chitin of the side 
walls of the canal thins abruptly and in material cleared with caustic 
the proboscis canal appears to terminate with a spur on either side. 
There is no real point of demarcation, however, between the pro¬ 
boscis canal and the pharynx as I have limited them, except the 
completion of the tube as the mouthparts join the head and the for¬ 
mation of these seeming spurs. The chitin of the floor of the canal 
is already thin and so harmonizes with the thinned walls. On the roof 
of the canal the heavy chitin extends for a considerable space into 
the head, thinning out gradually from the sides toward the midline, 
and so forming a tongue of heavier chitin amid the weaker chitin. 
Nuttall and Shipley’s description of this structure, anterior hard pal¬ 
ate in Anopheles as “somewhat in the form of a trowel 7 ’ is equally 
vivid for Culex, since its arch is steeper than the arch of the 
pharynx roof generally (pi. 13, fig. 5). Just before this palate 
terminates, its surface is roughened by a few minute conical spines. 
The proboscis canal receives immediately anterior to the “ spurs” at 
its proximal end, a pair of muscles from the alae of the clypeus. 
These are the “epipharyngeal muscles ” (Annett and Dutton, : 01 ) 
and the region of their insertion closely corresponds to that 
