154 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
flies with a similar succession of proboscis canal, subclypeal pump, 
and extensive esophagus, the differentiation of the subclypeal tube 
into two regions appears'to be wanting. In contrast to the arrange¬ 
ments in these flies, the Tipulidae (pi. 14, fig. 18) have a chitinous 
“pump” in the region of the brain (pump) and the esophagus is 
restricted to .the extreme rear of the head. The Culicidae (pi. 14, 
fig. 17) resemble this last mentioned family with the exception that 
the “pump” is dilated behind the nerve-collar instead of being 
of nearly uniform diameter throughout its length. The Simuliidae 
possess a “pump’’ which is not markedly dilated at any point, but 
it is distinctly divided into a preneural and a postneural portion. 
This subdivision foreshadows the arrangement found in the Asil- 
idae and Tabanidae (pi. 14, fig. 19). Here the postneural part of 
the “ pump ” is vestigial while the preneural part is strongly devel¬ 
oped. If a nomenclature is to be satisfactory for all cases it clearly 
must take into account three differentiated regions of the stomo- 
daeum, in addition to the unspecialized esophagus: the proboscis 
canal of the labrum ( pc ), the subclypeal tube ( plx ), and the more 
posterior chitinized “pump.” Of these the subclypeal tube and 
the pump may be subdivided. Two additional factors must be 
considered. The subclypeal tube appears to be an essentially homol¬ 
ogous structure throughout the group of the flies and the pump 
probably corresponds to the anterior end of the elongate esophagus 
of those flies where only a subclypeal tube (pli) is differentiated, 
e. g ., Muscidae. A system of names which groups the subclypeal 
canal and pump under a single expression is therefore inadvisable, 
as for example Christophers’ and Annett and Dutton’s accounts 
where these regions collectively form the “ pharynx ” or Hurst’s 
description in which the terms “ buccal cavity ” and “ pharynx ” 
are used indifferently for all the specialized intracephalic stomo- 
daeum. 
Two systems of nomenclature for the Dipteran stomodaeum which 
are free from the objections cited, exist. The older seems to have 
come into being by simple extension of the names given to the parts 
in Musca, i. e., “pharynx” for the subclypeal tube, and “esophagus” 
for all the remaining fore gut. Thus Meinert ('81) calls the pump 
of Tabanus and Asilus “pars prior oesophagi” or “pars tumida 
oesophagi.” With Culex or Tipula this region is simply “oesopha¬ 
gus.” Dimmock (’81) with respect to the parts in Culex, the most 
