186 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
nuclei, older and younger, remain side by side until the twentieth 
hour is reached, when the contractile substance, hitherto hostile to 
haematoxylin, stains readily with it and all the nuclei are larger 
and reticulate — the imaginal condition. The final increase in the 
amount of the contractile substance and the complete attainment 
of the imaginal staining reaction are soon reached. The relation of 
the larval to the imaginal muscles is as follows: — 
o 
Larval Series. 
Retractors of the pharynx. 
Lateral muscles of pharynx. 
Elevators of the dorsal plate. 
Anterior dilators of the esophagus. 
Posterior dilators of the esophagus. 
Lateral dilators of the esophagus. 
Imaginal Series. 
Ascending pliaryngeals. 
Lateral pliaryngeals. 
Muscles of the valve. 
Anterior dorsal dilators of antlia. 
Posterior dorsal dilators of antlia. 
Lateral dilators of antlia. 
Probably only the posterior portion of the muscle complex that 
I have called the lateral dilator of the esophagus, gives rise to the 
lateral dilator muscles of the imago’s antlia, the anterior portion 
being histolyzed. The hvpopharyngeal muscles of the adult are 
derived from the fibers beneath the hypopharyngeal sclerite. Those 
muscles dorsad of the alimentary canal which have forerunners 
among the larval muscles appear from the twenty-fifth hour onward 
and the clypeus begins to differentiate at this time (pi. 17, fig. 58). 
The esophageal valve of the new-formed pupa is partly drawn out 
of the cardia, so that the annulus of regenerative cells {arm) lies in 
line with the walls of the cardia and the upper bend of the valve 
has been shifted to a point low down on the reflected face. The 
regenerative annulus also has widened, probably through modifica¬ 
tion of adjacent cells of the epithelium of the valve. In a pupa five 
hours old (pi. 16, fig. 38) the valve is completely withdrawn from 
the cardia. The regenerative annulus is very prominent and the 
annular muscle of the valve {ann m) has begun to degenerate in 
advance of the histolysis of the muscle-coats generally. An hour 
later, the regenerative annulus is represented by a low circular ridge 
of columnar cells which projects into the lumen of the esophagus 
just [above the cardia. The valve lies immediately cephalad as a 
low ring-fold of the wall of the gut, girdled externally by the 
