1914] Tower—Mechanism of the Mouth Parts of the Squash Bug 105 
its anterior end except for the two openings of the salivary ducts 
(sd) on its ventral side and the opening into the salivary pump 
canal or efferent canal] (ec) in its anterior dorsal surface. Within 
the cylinder is a valvular flap (iv) which is attached posterior to 
the salivary ducts. This valve covers these ducts and allows the 
salivary juices to enter the cylinder from the salivary ducts, but 
does not permit it to flow back. The dorsal opening is closed by 
a long valvular flap (ov), attached to the dorsal wall of the efferent 
canal, which extends forward. This allows the salivary fluid to 
pass out of the pump and into the efferent canal, but not to return 
again into the cylinder. Normally the cylinder is nearly filled by 
the piston head or plunger (pl), see Pl. 1 f. 5, to which is attached 
anteriorly and laterally the elastic flexible membranous posterior 
wall of the cylinder. Posteriorly the piston head or plunger is 
attached to a piston rod to which are attached two large muscles 
(k) which diverge posteriorly and are attached to the posterior 
ventral region of the head and also by few muscle fibres to the 
ventral surface of the lobes of the tentorium. ‘These muscles in 
contracting draw the plunger back creating a vacuum in the cylin- 
der. This closes the dorsal outlet valve and opens the ventral or 
inlet valves causing the pump cylinder to fill with saliva from the 
salivary ducts. When the muscles relax, the elasticity of the pos- 
terior wall of the cylinder draws the plunger back into place, there- 
upon the ventral valves are closed and the dorsal one is opened 
and the saliva is forced out through the efferent canal and down 
the salivary canal in the sete and into the plant tissues. 
It seems not unreasonable to suppose that these salivary juices 
act on the plant cells chemically, possibly as a poison, and cause 
them to yield their juices more readily, although this point has 
not yet been investigated. 
The efferent canal after leaving the pump cylinder extends for- 
ward in a straight line (being supported by a portion of the chiti- 
nous tentorium and gradually itself becoming chitinized) until it 
reaches the membranous sheath about the sete which it penetrates, 
and then unites with the lower of salivary canal in the sete. 
The tip of the efferent canal which is trough-like and chitinized 
enters the salivary canal at the separation of the maxillary setz 
and lies on the ventral surface of the salivary canal. The union 
is made air tight by the chitinous tentorial support of the efferent 
canal and the membranous sheath. 
