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 



