Mr. Garner on the Ner-vous Si/stem of Molluscous Animals. 49l 



plying the mantle (C). The branchial ganglion (H.), situated as in Aplysia, 

 does not send its filament (/.) as a distinct nerve up to the brain, but it passes 

 through the ganglion supplying the mantle. The two cerebral ganglia (A.) 

 are here lateral. The pedal ganglia are connected both with the sentient 

 lobes, and with those supplying the mantle, as will be found generally the 

 case. A suboesophageal nerve completes the ring, and combines the pairs of 

 ganglia; and the cerebral ganglia as usual give the nerves forming the pha- 

 ryngeal ganglia. 



The spiral Gasteropoda present considerable variety in their nervous system. 

 It may be premised that in them we shall (with a few exceptions, where we 

 only find two,) observe four nerves originating from the superior lobes, when 

 the ganglia of the ring remain far separate, but from the posterior part of the 

 inferior expanded portion of the ring in the higher Gasteropoda. The two 

 external ones are the nerves of the mantle, analogous to those we shall see in 

 the Sepia (and it is to be remembered that the mantle is an important part in 

 respiration) : the two internal ones are analogous to the branchio-visceral 

 ones of the same animal. The branchiae are sometimes supplied by one, 

 sometimes by the other, and sometimes by both ; but in the higher Gastero- 

 poda entirely by the latter, as in Cephalopoda -, and we shall therefore call the 

 internal pair, arising from the posterior point of the inferior portion of the 

 brain in the higher Gasteropoda, the branchio-visceral when the animal is 

 aquatic, or pneumogastric when terrestrial. From theSe latter, filaments 

 go to the viscera, and often form a ganglion at or near the stomach. The 

 nerves of the mantle originate external to the preceding, and sometimes wholly 

 or in part supply the branchiae. From the shape of the spiral Gasteropoda 

 these are more or less twisted in their course. They may be well termed ex- 

 ternal respiratory, as they supply the mantle, siphons, and roof and floor of 

 the respiratory sac, and often the branchiae more or less. The shell-muscles 

 partly receive their nerves from one of these pairs, partly from the pedal 

 ganglion. 



The nervous system of lanthina (fig. 7.) is one of the most simple of those of 

 the spiral Gasteropoda. In it we have a lateral ganglion (A.) on each side, 

 considerably removed from each other, giving origin to the nerves of the eyes 

 and tentacles (g.) and lips (».), and posteriorly each ganglion sends off three 



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