Mr. Goodsir on the Anatomy of the Limneus involutus. 23 



genus Bulla than of the other Limnei, seemed so highly in- 

 teresting, that I conceived that the mere description of it 

 would be of comparatively little value without that of the ani- 

 mal. Its dissection was most kindly undertaken by Mr. Good- 

 sir, to whom I am indebted for the following description, and 

 the admirable drawing which illustrates it. 



Ci In structure the Limnaus involutus resembles the other 

 species of the genus. When its organs are compared with 

 those of the L, stagnalis as described and figured by Cuvier, 

 they are found, with the exception of the nervous collar, and 

 the reproductive organs, to be nearly identical in arrange- 

 ment and structure (Plate I. fig. 2.). 



u In his memoir on the Limnceus and Planorbis, Cuvier de- 

 scribes the supra-cesophageal portion of the nervous collar as 

 consisting on each side of three small globules, connected 

 mesially by a narrow portion ; of an infra-cesophageal gan- 

 glion composed of three masses, and of a small ganglion at the 

 junction of the buccal apparatus and gullet. In the L. invo- 

 lutus the nervous collar presents the following arrangement 

 (fig. 3.). On each side of the gullet and buccal mass, there 

 are two fusiform ganglia (a a), connected superiorly by a 

 straight narrow commissure (b), and inferiorly by four small 

 lateral (c c c c) and two large median ganglia (d d). Ante- 

 rior to these and concealed by the buccal mass are two large 

 ganglia (e e), connected mesially to one another, and laterally 

 to the middle of the lateral ganglia (a a), having no connexion 

 with the six posterior ganglia. The masses (« a) give off near 

 their anterior extremities two nerves, which run forward along 

 the inferior surface of the buccal apparatus, and terminate in 

 two small ganglia {ff), which are connected by a filament, 

 and distribute nerves to the buccal mass and oesophagus. The 

 lateral ganglia therefore have one superior commissure, con- 

 sisting of a simple cord, and two inferior commissures, the pos- 

 terior containing six ganglia, the anterior two. The lateral and 

 the six posterior ganglia give off all the nerves described by 

 Cuvier; the two anterior connecting masses supply the mus^ 

 cular bundles in their neighbourhood. 



" The arrangement of ganglia described above is not peculiar 



