MESSRS. HANCOCK AND EMBLETON ON THE ANATOMY OF DORIS. 
237 
the nerve-tubes and nerve-vesicles, goes to confirm what we have elsewhere said 
respecting the corresponding parts in JEolis, and support the now almost universally 
received ideas on the subject of the relation of these parts to each other in the higher 
animals. 
Extensive traces of the sympathetic system have been detected in several other 
species of Doris as well as D. tuberculata ; and it is interesting to remark, that on the 
CESophagus, stomach and genitalia of Eolis papillosa ganglia and nerves of the same 
system have been observed. The same system has been seen in Avion ater, and 
there can be little doubt that it will be found in all the higher Mollusks. 
It is worthy of notice, that in these Mollusks we have found no special relation 
between the nerves of the sympathetic system and the blood-vessels, such as are well 
known to exist in the Vertebrata, the only exception being that the nerve (g) from 
the visceral cerebro-spinal ganglion that goes to the branchial plexus, and to the two 
hearts, gives branches to the aorta and one of its divisions ; on each of these branches 
appears a small ganglion. It is possible that on further and more minute scrutiny 
plexuses on the great vessels at least may be discovered. 
After this detailed account of such a complicated system of visceral nerves, few 
perhaps will be disposed to doubt that we have here a true sympathetic nervous 
system. The fact, however, of the existence of ganglia and intercommunicating 
nerves forming plexuses, the mode of disposition of these networks upon the organs, 
their connections with the principal nervous centres grouped around the oesophagus, 
and lastly, the microscopic structure of both nerves and ganglia, all combine to prove 
the correctness of what we have advanced. 
Assuming it, then, as proved that the system before us is a true sympathetic or 
splanchnic nervous system, let us now see what light this new fact is capable of 
throwing upon the physiology of the ganglia about the oesophagus. Although 
hitherto physiologists have seemed to concur in the belief that somehow or other the 
oesophageal centres president the same time over the functions of both animal and 
organic life, still there have been differences of opinion as to the mode of the assign- 
ment to the individual ganglia of functions apparently so different in nature as those 
of the cerebro-spinal and sympathetic systems. The principal theories to be met 
with are three ; first, that all the ganglia, both those above and those below the 
oesophagus of the Mollusca, perform in some way or other the entire functions of 
cerebro-spinal and sympathetic systems ; second, that the supra-oesophageal ganglia 
represent the cerebro-spinal, and the infra-oesophageal the sympathetic system of the 
Vertebrata ; third, that whilst the two series of ganglia in the Mollusca are the 
counterparts of nearly all the cerebro-spinal in the Vertebrata, the nerves lying along 
the oesophagus and going to the stomach, represent the “ par vagurn ” or the sympa- 
thetic” or the visceral nerves.” 
The discovery of the true sympathetic nervous system not only proves that the 
third theory here noticed is that which most nearly approximates to the truth of 
