148 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Imago. 
Head and mouthparts. — An extended description of tlie exter¬ 
nal anatomy of the mosquito does not come within the scope of this 
paper. A few points with respect to the head, however, must be 
noted. The part of the head that lies in front of the large com¬ 
pound eyes is inflated above to form a rectangular box, which is 
called the clypeus. This seems to correspond to the “face” of 
other flies. A vertical furrow is impressed into the anterior face 
of this box. At the foot of the furrow a boss of chitin for muscle 
insertion projects into the cavity of the clypeus, while near the roof 
of the box on either side a short chitinous ala also enters the cavity. 
Ventrally and at the sides, the pre-ocular region of the head is 
rounded and forms as it were an imperfect cylinder, at the summit 
of which the mouthparts arise, nearly at one level. The anterior 
wall of the clypeus lies forward of this point by one half of the 
length of the box in the female insect and nearly two thirds of the 
length in the male. The postocular or epicranial region of the head 
is extensive in the female but truncate in the male mosquito. 
Within, the head is strengthened by a mesial crest which con¬ 
tinues from the level of the antennae along the roof of the head to 
the border of the occipital foramen. It is also braced by two 
hollow cylindrical struts which pass from the ventral border of 
the occipital foramen to the cheeks. I shall refer to these struts as 
tentoria, without intending to imply any necessary morphological 
connection between them and the analogous internal head braces of 
other insects. Among the hies, hollow tentoria similar to those of 
the mosquito are found in Chironomus, Anopheles, and Simulium. 
They appear to be wanting in many families, as, for example, the 
Tipulidae, Asilidae, Dolichopodidae, and the Muscidea. The Ta- 
banid hies have solid tentoria with somewhat the same relations as 
the hollow struts of the mosquito. In the female of Culex the ten¬ 
toria arise in front of the border of the occipital foramen and ascend 
at an angle of twenty-hve degrees with the floor of the head. Each 
strut has a short spur near the lower end, to which no obvious func¬ 
tion can be assigned, and above as the cheeks are approached, hares 
out into an irregular funnel-shaped “ head.” In the male mosquito 
the struts arise from the border of the occipital foramen, and the 
