THOMPSON : ANATOMY OF MOSQUITO. 
183 
fig. 36, epi). Structureless debris from the strands of protoplasm 
that formed the cores of the epipharyngeal and fiabellal setae fills 
the diverticula and spreads into the buccal space. In front of the 
curve where the potential proboscis canal enters the buccal cavity, 
the salivary duct opens. The pharynx retains something of the 
form which characterized it in the larva and the less markedly col¬ 
umnar epithelium as contrasted with the epithelium of the buccal 
cavity. The roof has evidently shortened, since the dorsal pharyn¬ 
geal muscles are crowded toward the elevators of the palate, but 
this and other changes in the relation of organs cannot be accu¬ 
rately formulated, owing to the lack of fixed points from which 
to measure. 
After the third hour of pupal life (pi. 17, fig. 56) the lumen of 
the buccal cavity opens again. It is soon freed from detritus and 
remains clean during the rest of the metamorphosis. The fiabellal 
pits steadily diminish in size and finally fade out. The cells of the 
epipharyngeal pit histolyze and before the tenth hour is passed have 
dissolved into a mass of broken elements. This lies within the 
cavity of the head, completely cut off from the buccal cavity (pi. 17, 
fig. 57, epi ), and is slowly absorbed without the intervention of pha¬ 
gocytes. Seemingly the separation of the degenerating epithelial 
pouch from the buccal cavity (pi. 16, fig. 39) is accomplished by an 
inpusliing of the adjacent epithelium rather than bv a proliferation 
of cells at the margin of the pit. Mitotic figures are absent. It is 
not impossible, however, that some of the epithelium which closes 
beneath the degenerating cells and cuts them off from the lumen of 
the buccal cavity is derived mediately or immediately from the epi¬ 
thelium of the epipharynx as it is destroyed. If this is so, and 
the epipharynx of the mosquito wriggler is a true epipharynx, part 
of the anterior hard palate of the imago is epipharyngeal in origin. 
And in such a case the small conical setae near its apex might gain 
a morphological value as epipharyngeal structures This will not 
affect the character of the labrum as a simple and not a compound 
organ. 
While the changes described have been taking place, the pharynx 
has become cylindrical and the cells of its epithelium now exactly 
resemble the cells of the epithelium of the buccal cavity. It is not 
clear how this alteration is accomplished. No mitotic figures can 
be found and no waste is given off into the lumen of the gut. The 
