188 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
the stomodaeal epithelium is partially destroyed at least and is rebuilt 
from scattered regenerative cells, as well as from the imaginal ring 
(van Rees, ’88). In Culex the esophageal epithelium seems to 
suffer no loss of cells and the regenerative annulus gives rise to the 
imaginal esophageal valve by simple remodeling. 
The salivary glands frequently begin to degenerate before pupa¬ 
tion occurs and the destructive processes advance rapidly during 
the first hours of pupal life. The cytoplasm of the epithelial cells 
becomes more and more spongy, large vacuoles appear here and 
there, and the nuclei decrease in size. Meanwhile the small re¬ 
generative cells at the neck of the gland are steadily increasing in 
number. By the twentieth hour the glands have shifted to a more 
ventral position and the regenerative epithelium stains deeply with 
haematoxylin, a characteristic of regenerative epithelium generally. 
The nuclei of the gland cells are now still more diminished in size 
and the vacuolization is extensive, especially near the belt of regen¬ 
erative cells. Frequently cells are so distended by vacuoles that 
they obliterate the lumen of the gland. About this time the 
imaginal salivary glands appear as three small cylinders developed 
from the regenerative epithelium. As soon as these form, the 
larval glands histolyze completely, become a mass of granular 
detritus filled with fragments of chromatin and are absorbed with¬ 
out phagocytosis in five or six hours. In their places on either 
side of the thorax lie the three slender tubes of the imaginal 
glands. Just before the mosquito leaves the pupa case the glands 
enlarge, shift to the adult position beneath the alimentary canal, 
and the central and lateral acini become unlike. Whether the 
final increase in size is due to increase in the number of compo¬ 
nent cells or only to growth of cells already present, could not be 
determined. After the emergence of the fiy, the nuclei of the cells 
enlarge slightly, and the cells become distended with the stored sali¬ 
vary secretions until three times their former dimensions. 
The epithelium of the cardia and stomach is totally histolyzed 
and a new epithelium is formed from regenerative nuclei which 
appear among the older cells. This course of development has 
been observed for the midgut of all flies whose metamorphosis has 
been studied (Korscheldt and Heider, ' 99 ). The larva of Culex 
reaches pupation with degenerative and regenerative processes well 
established. The cytoplasm of the epithelial cells is vacuolated, 
