THOMPSON : ANATOMY OF MOSQUITO. 
153 
The head of the Anopheles mosquito is relatively higher and 
broader in the epicranial region than the head of Culex and the 
pre-ocular region slopes downward. This makes the muscles run 
forward at different angles from those in Culex and sections of the 
two forms appear somewhat unlike, although, with a single excep¬ 
tion, the same muscles are present in both. The muscles of the 
mouthparts and head, outside of those supplying the alimentary 
canal, differ from the muscles of Culex as follows. The retractors 
of the maxillae arise more laterally and fully 30 /x caudad from the 
bases of the tentoria, so that their origin is wholly from the walls of 
the head and not partly epicranial and partly tentorial. The poste¬ 
rior or apodeme ends of the protractors of the maxillae also, lie far¬ 
ther back and the upper or tentorial ends are in the same level as 
the double retractor muscle. Hence both protractor maxillae and 
double retractor muscles may be present in one section, which is not 
the case with Culex where the origin of the protractors is distinctly 
caudad from the origin of the double retractors (pi. 13, figs. 7, 15). 
The subocular muscles are much larger, and arising farther back in 
the head, they are less likely to be mistaken for fibers of the re¬ 
tractors of the maxillae. They are inserted on the tentoria immedi¬ 
ately caudad of the origin of the double retractor muscles, near the 
insertion of a pair of minute transverse muscles, not represented in 
Culex, which arise on the walls of the epicranium dorsal to the 
origin of the anteriormost lateral dilator of the esophagus. 
The fore gut. — The stomodaeal portion of the alimentary tract 
of insects is subject to great variations with respect to the number 
and character of the regions that are differentiated in it. It may 
well be considered doubtful if homologies between regions can legit¬ 
imately be sought beyond the limits of any one order. Hence a no¬ 
menclature for the various parts need only be self-consistent within 
a single order and may properly be subject to individual prefer¬ 
ences. The stomodaeum of the imagoes of the Diptera offers 
especial obstacles to the establishment of a system of names that 
shall meet all conditions, for there is a considerable range of vari¬ 
ation within the group. For example, in Musca (pi. 14, fig. 16) 
the labral or proboscis canal (pc) is succeeded by an intracephalic 
subclypeal pump ( ph ) which shows distinct anterior and posterior 
regions. Then the esophagus (oes) commences and hence extends 
through the circumesophageal nerve-collar or “brain.” In other 
