184 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
loss of histological and structural distinctions between the buccal 
cavity and pharynx leaves as landmarks for the entrance to the 
pharynx (pi. 17, fig. 56, *) only the cingulum muscle below and the 
anteriormost dorsal pharyngeal muscle above. The dorsal mark is 
open to the objection that this muscle lies behind the actual bound¬ 
ary ; and the relations in this neighborhood are obscured also by 
the retraction of the fiabellal hypodermis back to the epipharynx — 
which does not seem to have moved much — and by the shortening 
of the roof of the pharynx. These criteria enable us to judge 
the morphological value of any comparison between the limits of 
the larval and imaginal fore gut regions. Nevertheless, it will be 
interesting and perhaps not unprofitable to work these out (pi. 17, 
fig. 56-58). Roughly speaking, that part of the pupal bucco- 
pharynx which is in front of the anteriormost dorsal pharyngeal 
muscle and the cingulum muscle represents the larval buccal cavity. 
Ventrally, the boundary early becomes indistinguishable owing to 
the loss of the cingulum muscle, but dorsally a slight bend comes 
in near the point where the two regions meet (*). This bend 
coincides with the rear border of the soft palate of the imago. 
Pharyngeo-esophageal boundaries are not developed in the larva 
ventrally, but dorsally the insertion of the retractors of the pharynx 
(retr ph) marks the rear of the pharynx. These muscles metamor¬ 
phose into the ascending pharyngeal muscles of the imago (asc ph). 
The anterior dilator muscles immediately caudad become the anterior 
dorsal dilator muscles of the antlia of the imago. The epipharyngeal 
pit lies at first above and then forward of the marked curve in the 
gut. This curve remains after the epipharynx and its muscles have 
vanished and the front wall of the clypeus forms distad of it. So, 
unless it shifts position markedly, for which there is no evidence, 
the epipharyngeal muscles of the imago insert on the roof of the 
buccal cavity very near the point occupied by the larval epipharynx. 
The esophagus undergoes no metamorphosis beyond the destruc¬ 
tion and regeneration of the muscle-coats, the differentiation of the 
antlia at its anterior end (pi. 17, fig. 57), and certain changes which 
involve the esophageal valve. The esophageal epithelium is handed 
intact to the imago, probably with an increase in the number of the 
component cells. The muscle-coats histolyze about the eighth hour 
and are replaced somewhat later by the imaginal muscles. The 
process could not be studied in detail because of the minute size of 
