172 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
is developed in the dorsal plate and very possibly serves as a check 
( ores ). 
The pharynx has an elaborate musculature. The two halves of 
the dorsal plate are united by transverse or oblique bands (dor 
ph) which attach to a longitudinal sclerite developed on either 
side of the median fold. A pair of diagonal muscles (pi. 15, figs. 
30, 33, ding) reach the pharyngeal crests near their posterior ends, 
from origins on the roof of the head, in each case on the side 
opposite to that of the insertion. At the summit of their curve the 
crests receive lateral muscles (lat m) from the scythe-shaped areas 
on the walls of the head, while nearer the border of the buccal 
cavity, several lesser lateral muscles (less lat) reach the dorso-lateral 
walls. At their approximated posterior ends the crests are bound 
to the epicranium by stout muscles, the retractors of the pharynx 
(pi. 15, figs. 80, 32). The hinder parts of the dorsal plate furnish 
insertion for two elevators of the dorsal plate (el dp ), which descend 
from the epicranium. The lateral and ventral walls of the pharynx 
and the walls of the esophagus generally possess a well developed 
circularis muscle-coat and one of the most characteristic of the 
pharyngeal muscles is probably only a specialization of the circu¬ 
laris. This muscle girdles the pharynx from the angle where the 
crests meet, along under either crest and beneath the floor below. 
It may be called the girdle-muscle or cingulum (pi. 15, figs. 32, 35, cm). 
In front of the point where the cingulum passes under the floor of 
the pharynx, two slender muscles arise and extend back to the walls 
of the epicranium near the occipital foramen. These are the ventral 
retractors of the pharynx. They run in company with a number of 
slender muscles which emerge at intervals from beneath the circu¬ 
laris of both pharynx and esophagus. The complex that is formed 
by these muscles may be called the lateral dilator of the esophagus 
(lat dil oes). There are also two pairs of dilator muscles that 
insert on the dorsal wall of the esophagus (pi. 15, fig. 32, ant dil , 
dor dil). The larger of these he above the supra-esophageal gang¬ 
lion and closely parallel the retractors of the pharynx; the smaller 
lie beneath the ganglion. 
When a wriggler is feeding the significance of the peculiar phar¬ 
ynx and musculature becomes apparent. It will be noted that the 
pharyngeal crests rapidly approach and separate so that the dorsal 
plate must be constantly infolded and withdrawn. The great fans 
