162 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
drical than the antlia of Culex. This point of difference is of 
interest in connection with the varied specialization of the antliae 
in the Diptera. On a basis of their pumping mechanisms the group 
can be separated into two main groups, which may be termed 
monantlial and diantlial. The former division includes the Musci- 
dae (pi. 14, fig. 16), the Syrphidae, and other families the members 
of which possess only the pharyngeal pump. The diantlial group 
have both a pharyngeal pump and an antlia. Among these Hies 
several forms of antlia are found. For example, Culex (pi. 14, 
fig. 17) and Anopheles have an antlia which is best developed 
behind the “brain,” i. e., it may be described as postneural in type. 
As already noted, the pump of Anopheles is less markedly postr 
neural than that of Culex, approaching what may be called the 
amphineural type, where it is nearly cylindrical throughout. The 
Tipulidae are perhaps the best example of this type of antlia (pi. 14, 
fig. 18, pump). Simulium, while amphineural with respect to the 
form of its antlia, has this region differentiated into distinct pre- 
and postneural sections. The antlia of the Tabanidae (pi. 14, fig. 
19) and the Asilidae is not only subdivided as in Simulium, but 
the preneural part alone is functional, the post-neural section being 
rudimentary. This type may be called preneural. 
The tracheation of the head is interesting with respect to the 
supply to certain parts of the alimentary canal and muscles. Thus 
the extensive tracheal supply to the elevators of the palate shows 
that these muscles are of considerable use, and that the pharynx, 
although overshadowed by the great esophageal pump, is yet by no 
means unimportant as a suctorial bulb. The thoracic portion of the 
alimentary canal is paralleled on either side by a tracheal trunk. 
From either trunk two tracheae are given off into the head, the 
external and internal tracheae (pi. 13, fig. 12). These lie close to 
each other until they have passed the dilator muscles and then part 
company. The external trachea ascends into the cleft between the 
optic ganglion and the “brain” (pi. 13. fig. 10), supplies these nerv¬ 
ous masses and the protractor muscle of the maxilla, and then 
breaks up into branches some of which run in the mesial plane of the 
clypeus to supply the labral muscle and the elevators of the palate. 
The internal trachea follows the ascending line of the tentorium and 
its terminal twigs reach the head of the strut. But before this point 
is attained, the trachea has spent itself in two large branches. The 
