STRUCTURE AND RIOLOGY OF SCHIZONEURA I.ANIGERA. 673 
and posteriorly by the hypopliarynx (h.) and proboscis (pr.). 
Laterally it is bounded by the lateral lobes of the clypeus, 
mandibles (md.), and the inaxillte {mx.), and leads into the 
suction canal formed by the fusion of the maxillte. 
The Pharynx. — The mouth leads upwards into the pharynx. 
This structure is a distensible chamber lined with cliitin, which 
is continuous with the cuticle of the body. Its posterior or 
ventral wall is strengthened by a stout layer of chitin, but its 
anterior wall is composed of flexible membranous chitin. As 
seen in transverse sections (figs. 12-20) the pharynx is 
crescentic in shape, its greatest transverse diameter being 
near the oral end. Its walls in this region are thickened to 
form two hollow, dome-shaped protuberances {p.p.) or ridges, 
the “Naroiden” of Dreyfus (1894) in Phylloxera. The 
lumen of the pharynx in this region is very narrow, and 
divaricator muscles (m. ph.) pass from its dorsal wall to the 
wall of the clypeus. Two folds of chitin extend from the 
clypeus to the wall of the pharyn.x protuberances, with which 
they fuse. 
The pharynx is well supplied with muscles. Attached to 
its anterior flexible wall are several bands of divaricator 
muscles, which extend to the anterior wall of the clypeus. 
These muscles are divided into fine tendons at their attach- 
ment on the chitinous walls of the clypeus. By means of 
these muscles, the anterior wall of the pharyu.x is drawn 
outwards and the lumen of that structin-e is greatly enlarged, 
the plant juices being drawn into it through the mouth. I 
have pointed out that the lumen in the region of the pharynx 
protuberances is very narrow, and ventrally has stout chiti- 
nous walls. When the divaricator muscles of this region 
are relaxed, the entrance into the pharynx chamber is almost 
closed, preventing the plant juices from returning into the 
mouth. As the other divaricator muscles of the pharynx are 
i-elaxed,the anterior wall of that structure, on account of its 
flexibility, tends to regain its original shape, and the cavity, 
being thus greatly reduced in size, the juices are forced 
backwards into the oesophagus. 
