1908.] 



ASPIDOBRANCH GASTROPOD MOLLUSCS. 



855- 



and the large ganglionic enlargement on its coui'se is associated 

 with the great importance and complexity of the accessory genital 

 organs in the ]Sreritid8e. 



Beyond this recto-genital nerve the visceral commissure in its 

 course from right to left is somewhat thinner than it is in the 

 region of the ganglionic swelling just mentioned, but it remains 

 invested with a coating of nerve-cells, and is only gTadually and 

 slightly enlarged in front of the uropore to form the visceral 

 ganglion described and figured by all previous authors. I must 



Text-fi^. 172. 



cm.r. 



A dissection of Nerita plexa, showing the coui'se and distribution of the visceral 

 nerves and the visceral, branchial, and osphradial ganglia : semidiagrammatic. 



An, anus, hr.n, branchial nerve, cm.r, right columellar muscle. Cry.s, crystal 

 sac. CY, ctenidium. ^fZ, complex ot genital ducts and glands. ,^.^, genital ganglion. 

 ffn^, nei've passing to the spermatophore-sac. ffn-, nerve passing to the organs of 

 the genital complex, m^, anterior (pallial) branch of the branchio-pallial neive. m-, 

 posterior (branchial) branch of the branchio-pallial nerve, os, osphradium. os.j, 

 osphradial ganglion. Fh, pharj'ugeal bulb, sb.n, subintestinal nerve, sjy.ff, supra- 

 intestinal ganglion (identified as a separate ganglion only in IKerita plicata and 

 Faranerita gagates). sj;.m, supra-intescinal nerve. I7rj9, uropore. F^, right-hand 

 enlargement of the visceral ganglion. V-, left-hand enlargement of the visceral 

 ganglion. These two enlargements are much closer together than represented in the 

 figure ; the tissues Ij'ing between them have been stretched by turning back the 

 genital complex, and the middle part of the visceral ganglion is represented as if 

 stretched to a corresponding amount. It is almost invariably broken in actual 

 dissection. 



