Burgess.] 
226 
[October, 5, 
{the frontal muscles y 1ig\ires 1 and 2 f.m.) is attached. The con- 
traction of this muscle of course draws up the mouth roof, and 
thus forms part of the pumping mechanism we should expect to find 
in a sucking insect. The mouth floor on either side sends a process 
(figs. 1, 4, pr.) backwards and upwards into the cranial cavity, serv- 
ing for the attachment of another powerful pair of muscles (pr. m. 
figure 2, shown, but not lettered, in figure 1) lying just behind the 
frontal muscles, concerning whose function I am yet in doubt. They 
may be concerned in one, two, or perhaps all, of three operations, 
namely, to open the mouth lock, to tighten its grip, or to draw the 
middle portion of the mouth floor away from the roof. This last 
action is rendered possible from the fact that, while the mouth is 
held rigidly in position by the solid attachment of its corners, there 
is apparently a flexible transverse suture just beyond the process on 
either side. There remains only one muscle connected with the 
mouth proper, and that is a small transverse one crossing just 
above the opening of the pharynx, its function being to close the 
latter and to compress the mouth cavity. The muscles already 
Fig. 3. Longitudinal section through the mouth lock, X 125, m , Mouth. 
described evidently are competent of themselves to account for 
the sucking powers of the animal, but they are probably seconded 
by the action of the pharyngeal muscles. 
The pharynx (ph. in the figures) open into the mouth between 
the two processes above mentioned. In sections it is strongly 
defined by the junction of its delicate cuticular lining with the 
much thicker cuticle of the oral cavity, and also by its muscular 
investment, composed of annular and longitudinal fibers (see fig- 
ure 2). Like the pharynx, which I have already described in the 
case of the Lepidoptera, 1 it is hung in the cranium by suspensory 
1 Anniv. Memoirs, Bost. Soc. Nat. Hist. 
