THOMPSON: ANATOMY OF MOSQUITO. 
185 
the new elements. The antlia gradually forms during the first half 
of the second day of pupal life, but in common with other parts of 
the alimentary canal the characteristic imaginal intima with its divi¬ 
sion into plates is not developed until just before the fly emerges. 
This intima is secreted beneath the delicate undifferentiated pupal 
intima which lines the stomodaeum. The proctodaeum similarly 
has a pupal intima beneath which the imaginal intima is secreted. 
The lumen of the esophagus remains clean during the metamorpho¬ 
sis, except at the posterior end, where granular rubbish containing 
chromatin is found, seemingly drifted in from the cardia. 
All the muscles of the head continue intact until the eighth 
or tenth hour and then histolysis occurs. But although small 
leucocyte-like cells can occasionally be noted, these are rare and 
there is nothing which definitely assigns a phagocytic role to them. 
The mandibular muscles, the depressors of the antennae, the mus¬ 
cles of the maxilla, the epipharyngeals, the retractors of the flabel- 
lae, the diagonals, the dorsal pharyngeal muscles, the ventral 
retractors of the pharynx, and the cingulum histolyze and are 
absorbed between the tenth and thirtieth hour of pupal life. The 
first imaginal muscles appear about the eighth hour with two bands 
of small dark myoblasts, probably the maxillo-labial muscles. By 
the seventeenth hour the sides and floor of the head cavity are trav¬ 
ersed by similar belts of small myoblasts. The ultimate source of 
the new cells is uncertain, owing to the minute size of the elements 
of both the larval and the imaginal muscles. From the moment 
of their appearance the new nuclei are closely associated with the 
dermis of the head and their cells resemble the small, dark cells of 
this epithelium. There is, however, nothing which would militate 
against applying van Rees’ (’88) interpretation of the muscle meta¬ 
morphosis of Musca to Culex. By this the new myoblasts would 
be derived from the nuclei of the larval muscles. 
The retractors of the pharynx, the elevators of the dorsal plate, 
the lateral muscles, and the anterior, posterior, and lateral dilators 
of the esophagus are worked over into imaginal muscles. The 
anterior esophageal dilators alter first and their metamorphosis may 
be taken as typical. A majority of the large reticulate nuclei 
become smaller, darken, and lose the reticulum ; others histolyze. 
Then a large number of small dark nuclei appear, perhaps derived 
from the older muscle nuclei by amitotic division. The two sets of 
