030 C. GORDON HEWITT. 
the internal side of the portion of the lateral tracheal trunk 
that is anterior to the commissure a branch arises, and running 
ventral to the pharyngeal mass it supplies the anterior end of 
the larva and the oral lobes. A branch that supplies the 
muscles of this region is given off external to the origin of the 
anterior commissure. Internal to the origin of the commissure 
two trachee arise ; the anterior branch enters and supplies the 
pharyngeal mass, and the posterior branch (¢r.’) enters the 
ganglion ventral to the cerebral lobes. In the fifth segment 
another internal tracheal branch enters the ganglion (tr.”). 
These tracheze which supply the ganghon appear to run 
chiefly in the peripheral regions, where they divide into a 
number of branches, the fate of some of these being interesting. 
These branches are extremely fine, and they arise, as I have 
previously mentioned, in association with a number of the 
segmental nerves with which they run to the body wall. 
6. Tue Vascunar System AND Bopy Cavity. 
The relations and structure of the vascular system of the 
larva are on the whole similar to those of the fly; there are, 
however, a number of modifications. 
The dorsal vessel, which includes the so-called “ heart,” is 
a simple muscular tube lying on the dorsal side immediately 
beneath the skin, and extending from the posterior tracheal 
commissure to the level of the cerebral lobes of the compound 
ganglion in the fifth segment. Its wall is composed of fine 
striated muscle-fibres arranged transversly and longitudinally, 
but chiefly in the latter direction. ‘The swollen posterior 
region (Pl. 33, fig. 31), which is called the heart, lies in the 
last three or four segments, its anterior limit. being hard to 
define, It consists of three distinguishable chambers, which, 
however, are not divided by septa. Three pairs of ostia (os.), 
each provided with a pair of internal valves (v.), are situated 
laterally, and place the cardiac cavity in communication with 
the pericardium, in which this portion of the dorsal vessel 
lies. There are three pairs of alar muscles controlling the 
