a carnivorous Tipulid larva. 247 
by a circular or slightly oval rim, composed of rather 
more than twenty scales. From this rim descends a 
cone or plug, with a thick and solid chitinous wall. 
Outside the cone is a chamber with a transparent chi- 
tinous wall, the vestibule. The cavity of the vestibule 
is crossed by many radiating and branched chitinous 
fibres, which spring from its outer wall. The stronger 
fibres are attached to the inner cone, but many of the 
smaller branches fail toreach it. There are no openings 
into the vestibule from without which I have been able 
to discover. Perhaps such exist, but I have looked for 
them in vain. The attached trachea leads from the 
lower end of the vestibule. A cylinder of epithelium, 
continuous with the tracheal epithelium at one end, 
and with the epidermis at the other, invests the outer 
surface of the vestibule. In the angle between this 
epithelium and the ordinary epidermis, I have found a 
zone of large cells forming a circular fold around the 
mouth of the spiracle. This closely resembles the rudi- 
ment of the anterior imaginal spiracle of Musca.* From 
the spiracles lead two good-sized trachee, which run 
along the dorsal surface of the body, giving off large 
branches to the body-wall and viscera. Segmentally 
arranged branches unite and give off ventral trunks, 
which supply the nerve-cord and other parts. 
The larva comes occasionally to the surface of the 
mud to breathe, and thrusts out the hinder end of its 
body. As both spiracles and tracheal gills are carried 
upon the last segment or segments, it is of interest to 
notice that the larva projects its tail sometimes into air 
and sometimes into water. They may be seen lying for 
a considerable space of time in either condition without 
any sign of uneasiness. When submerged, an air- 
bubble can often be seen attached to each spiracle. If 
prevented from leaving the water, they can live a 
long time, perhaps indefinitely, without visible incon- 
venience. 
It is, I think, instructive to compare the larva of 
Dicranota, with respect to its power of storing up 
oxygen, with the similarly situated Chironomus larva. 
Both are found in mud saturated with water, and so 
charged with decaying vegetable matter that it cannot 
* Cf. Lowne on the Blow-fly, pt. i., fig. 11, 3 (1890). 
TRANS. ENT. SOC, LOND, 1893.—PART III. (SEPT.) 8 
