Mr. Robert Garner's Malacohgical Notes. '611 



pods. Aplysia lias sometimes only one ganglion, in other 

 species two, to su])ply its duplicate but conjoined branchial 

 process and the protective mantle ; and the nerve crosses, as 

 just described. In liulUca aperta there is but one ganglion in 

 the posterior or respiratory section of the body ; in Akera bul- 

 lata there are three. Thus as the animal ascends there are 

 specific cerebral ganglia immediately connected with the above 

 functional nerves and ganglia. The posterior respiratory part 

 of the lower portion of the cerebral ring is always divided from 

 the anterior part, presiding over locomotion, by the transit of 

 the aorta ; or, rather, it is divided from the more anterior part 

 of the posterior centre, which supplies the siphonie nerves in 

 the Sepia, by the entry inwards of the vessel through the 

 cerebral ring, whilst that anterior respiratory part is separated 

 from the still more anterior locomotive centre by its exit. 

 The pharyngeal ganglia are seen in the higher mollusks to be 

 connected both with the sub- and supraasophageal centres ; in 

 Patella they send forward little nerves, going to the lips and 

 mouth, where they form two other little ganglia (olfactory) ; or 

 the latter may occur as a large ganglion {Sepia) intermedi- 

 ately between these pharyngeal ganglia and the brain. Taste 

 and smell appear to be connected with the last two pairs of 

 ganglia, hearing with the lower part of the cerebral ganglion, 

 sight with its upper part. The smell in the snail [Arion] may 

 be located in the whitish surface under the mouth, though 

 some think it resides in the tentacles. In some Cephalopoda, 

 as in Sepia^ the membranes (olfactory ?) surrounding the beak 

 are much developed. The organs of sight often appear as 

 mere specks on the brain itself, when the skin is pervious to 

 light {Scf/Ua'a, Boris). 



To facilitate a boundless production appears to be the first 

 object followed out in the structure of the reproductive organs 

 of Mollusca. A second is evoked by the necessity which tiiere 

 is for at least an occasional union between difi'erent individuals 

 of the same species, even when each contains in itself the 

 essential organs of both sexes (monoecious). 



A third object is but a part of the first, an ai'rangement 

 for the dis])ersion or safety of tlie young individuals till they 

 attain a suitable hahi'fat. The simj)le form of multiplication, 

 budding, or, more simple still, self-division, is, as said before, 

 a mode of increase only seen in the lowest mollusks, or rather 

 molluscoids ; and in them only can we find any trace of what 

 has been called alternate generation^ and which perhaps de- 

 pends upon the provision made to attain the third object above 

 mentioned. In some bivalves (in the fixed oyster, the scallop, 

 and in some freshwater mussels) the essential male and 



