246 Prof. L. C. Miall on Dicranota ; 
The pericardium is irregularly quadrilateral in trans- 
verse section, especially in the hinder part of the body, 
where it attains its greatest diameter. Thirteen pairs 
of alary muscles are attached to it, viz., two pairs to 
segments 5—10, both included, and one pair behind 
these. At the hinder end of the body an elliptical 
orifice, placed ventrally, admits blood from the body- 
cavity. Just in front of this the pericardium is attached 
to the intestine. The dorsal wall of the pericardium is 
also incomplete behind, and the blood, well aérated by 
the numerous trachee which supply the 12th segment 
and its appendages, may be seen to enter both above 
and below in a full stream. Extensions of the peri- 
cardial cavity occupy the bases of the alary muscles, 
and some, if not all, of these extensions lodge large 
cells in pairs. The pericardial wall consists of fibres, 
irregularly arranged but chiefly longitudinal, and over- 
laid by a multitude of small cells. 
The hinder part of the dorsal vessel is of larger diameter 
than the rest, and exhibits one (or perhaps three) val- 
vular inlets, but no distinct heart can be defined. At its 
extreme posterior end is a median inlet, flanked on each 
side by pocket or semilunar valves. A little further 
forwards, near the hinder end of the 10th segment 
behind the head, is a pair of ostia, or what look like 
them, though no blood corpuscles have been seen to 
enter here. The vessel is constricted at intervals, but 
shows no distinct chambers. Its wall consists largely 
of transverse fibres. In the cesophageal region a pair of 
ganglia are applied to the sides of the dorsal vessel, as 
in some other dipterous larvee. 
The blood is colourless ; its corpuscles are numerous, 
minute, and elliptical. 
The Respiratory Organs of the Larva. 
The larva of Dicranota, like all other Tipulid larve, 
except that of T'richocera,* has only one pair of spiracles. 
These are situated upon two rounded prominences on 
the dorsal surface of the 12th segment, and look back- 
wards and upwards. The structure of the spiracle is 
generally similar to that of some other dipterous larve 
(e.g., Ctenophora). The external orifice is surrounded 
* Osten Sacken, loc. cvt., p. 5. 
