238 Prof. L. C. Miall on Dicranota ; 
Set, which helps to close-in the side of the mouth. 
Beneath the mandibles are the long maxillary palps, 
each of which is provided with a sensory pit (?), a small 
filament, and a sensory spot. 
The submentum (pharyngeal plate of Meinert)* is 
divided by a median cleft, and its fore edge is armed 
with six sharp teeth.. Above it is a slightly bilobed 
plate, the mentum (labium of Meinert and other authors), 
which bears fine prominences along its free edge. The 
labrum is flexible, and armed only with very minute 
points. The top of the head is defended by a chitinous 
shield, which becomes very strong behind. From this 
shield descends, in the hinder two-thirds of the head, a 
median chitinous septum, which gives origin to muscles, 
and especially to the powerful muscles of the mandibles. 
Behind the antenne are two structureless patches of 
pigment, the eye-spots. ; 
The head is succeeded by the usual twelve seoments. 
The first of these (prothorax) is at first sight double, 
being transversely divided by a well-marked fold. This 
is, however, merely a crease, and results from the 
frequent retraction of the head. The rudiments of the 
imaginal legs and wings show which are the real 
thoracic segments of the advanced larva. 
The 6th, 7th, 8th, 9th, and 10th segments bear paired 
retractile processes, which resemble the pseudopods of 
caterpillars, and end in triple crowns of chitinous hooks. 
Beneath these are many regular rows of still smaller 
hooks, which form transverse rings. The terminal 
surface, enclosed by a circle of hooks, is inclined a little 
backwards in the two foremost pairs of pseudopods, a 
little forwards in the others. The pseudopods can be 
retracted completely by means of their attached muscles 
(fig. 13). Pseudopods of this sort (with much variety 
in details) occur in many creeping dipterous larve. In 
the tube-dwelling larve of Chironomus and T'anypus 
they are reduced to two pairs, viz., a prothoracic and 
an anal pair,t while in certain terricolous (Zipula) or 
natatory (Culex) dipterous larve they disappear alto- 
gether. 
The 12th segment bears three pairs of appendages, 
* Hucephale Myggelarver, fig. 94, c (Tanypus). 
+ In tube-dwelling larvee of Timeina the pseudopods may in like 
manner be reduced to insignificant rudiments, 
