DORSAL VESSEL OF THE IMAGO OF THE BLOW-FLY. 649 
The dorsal vessel of Eristalis is far larger and more easily 
examined than that of the Blow-fly, but has a very close 
resemblance to it, and in this insect I believe I have seen 
lateral thoracic vessels, which accompany the sinuses opening 
into the anterior end of the pericardium. 
Swinton has given a description of the dorsal vessel in 
Sphinx ligustri, and he represents a ventral sinus in the abdo- 
men, which he believed to be connected with the heart. This 
sinus, if it exist, is probably a venous sinus opening into the 
pericardium; and the short trunks, which he calls efferents, 
are all probably connected with the pericardial cavity, and are 
not efferent or arterial, as he apparently supposes, but afferent 
vessels. He cites Graber in support of his views, but Graber’s 
sinuses are afferent or venous. Such have been repeatedly 
described in different insects. 
I have been unable to detect any valves in the aorta, but 
such valves may probably be assumed to exist and would re- 
present the intra-ventricular valves of the intermediate part of 
the dorsal vessel of the larva (see page 91). 
Cardiac Nerves—The dorsal vessel undoubtedly receives a 
double nerve supply. The cardiac nerve is a continuation of 
the main trunk of the stomogastric, which lies between the 
chyle stomach and the pericardium. It can be seen as a fine 
white line on the ventrical surface of the pericardium, after the 
removal of the intestine, with an inch objective. About a milli- 
metre behind the edge of the mesophragma it divides into two 
lateral branches, which diverge to the edges of the pericardium, 
where they form a plexus and communicate with a great 
number of large ganglion cells (Pl. XLVI.). I have been 
unable to trace the cardiac inhibitory nerves from the thoracic 
ganglion, but they probably run in the stomogastric cardiac 
nerve, which they probably join as it passes beneath the meso- 
phragma or in the thorax, as stimulation of the cardiac nerve 
near the mesophragma produces a cessation of the pulsations 
of the dorsal vessel. 
The Nerve-Cells of the Pericardial Plexus are found in groups 
on the margins of the pericardial septum. They are stellate 
