176 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
parent. In sections the cells are clearly defined, their cytoplasm 
stains deeply, the moderate sized nuclei (11.5 g) are reticulate, and 
nucleoli are present. There are usually not more than five or six 
cells in the cross section at any point. As the wriggler nears the 
pupa stage numerous vacuoles occur in the cytoplasm of many of 
the gland cells, so that it appears spongy. This is a sign of degen¬ 
eration. Immediately prior to pupation, a belt of small cells forms 
at the neck where the gland narrows to meet the salivary duct. 
The cells of this belt are seemingly derived from the older cells of 
the neck of the gland and perhaps also from the epithelium of the 
outer end of the duct. They give rise to the itnaginal salivary 
glands. 
The midgut .— The midgut (pi. 16, figs. 37,45) of the larva 
shows three regions: cardia, a ring of eight caeca, and the stomach. 
The cells of the cardia stain more deeply than those of the caeca or 
stomach epithelium, but are otherwise similar. As already noted, 
the fore gutintima terminates at the “break” where the cardiac epi¬ 
thelium begins near the upper bend of the esophageal valve. The 
cardia is lined by the peritrophic membrane. In the mosquito the 
cardia of the larva gives rise to the cardia of the imago through 
a metamorphosis similar to that by which the stomach of the 
larva gives rise to the stomach of the adult. The esophagus and 
esophageal valve on the other hand, have a wholly different meta¬ 
morphosis, so that in Culex the cardia would appear to be unques¬ 
tionably a part of the midgut. This seems to be the case in 
Nematocerous flies generally, although the evidence is as yet not 
complete for any one form. The larva of Anopheles, Chironomus, 
and Simulium like that of Culex has a cardia whose epithelium 
resembles that of the stomach. The embryological development of 
the cardia of the Chironomus larva shows it to be of mesenteric origin 
in this case (Miall and Hammond, :00). Its relation to the cardia 
of the imago has not been studied. From Vaney’s (: 02) accoiint 
it would seem that the larva of Stratiomya belongs to this type 
and the cardia, “proventricule,” of the larva of Ptychoptera as fig¬ 
ured by van Gehuchten (’90) is more like stomach than esopha¬ 
gus in the histological structure of its epithelium. Occasionally no 
cardia is developed and in such instances the esophageal valve hangs 
directly into the stomach, e. g. Phalacrocera (Miall and Shelford, 
’97) and Dicranota (Miall, ’93). 
