54 PHYSIOLOGICAL SERIES. 



D. 51. A Slug (fslntu.c ru/W), laid open longitudinally along tin* 

 l>aek, and with the viscera removed, to show the nervous 

 -y-tem. Thecerehral ganglia are pear-shaped and situated 

 at some distance apart united by a commissure. They 

 innervate the same organs as in the Snail. The oesophagi -a 1 

 nervous ring is completed below the gut by a larger 

 ganglionio mass from which nerves radiate to supply the 

 body. The principal nerves are the two inferior ones which 

 extend on either side of the mid-line of the ventral surface 

 straight to the hinder end of the body, giving off branches 

 from their outer sides to the muscular foot. A small 

 asymmetrical ganglion is formed on the nerve that supplies 

 the heart and respiratory apparatus. The rabOBSOphagea] 

 ganglion is a compound body, formed, as in the Snail, by 

 the fusion of the pedal, pleura], and visceral ganglia. 



0. 0. 1304. Hunterian. 



D. 52. The same species of Slug laid open along the ventral 

 aspect, and with the viscera removed to show more 

 especially the subcesophageal ganglion and its nerves. A 

 bristle occupies the place of the (Esophagus. 0. C. 1305. 



Hunterian. 



D. 53. A Slug (Limax sp.) with the body-walls divided longi- 

 tudinally along the ventral surface, and divaricated to show 

 the nervous system in position. Preserved in Goadby 

 solution. 



D. 54. Two isolated specimens of the nervous system of a Pond- 

 Snail (Limncua stagnates). The central nervous sy>trm 

 although decidedly concentrated is much less so than in the 

 Land-Snail. The three pairs of ganglia that form the 

 circum-cesophageal ring (eerehral, pleural, and pedal) are 

 independent and joined together by short conunisMin-s and 

 connectives. The orthoneurotu visceral loop is extremely 

 short, yet its ganglia and the fibmn- >trand< that unite 

 them to one another and to the pleural ganglia can be 

 dearly distinguished. The distribution of the ner\e> that 

 arise from the various ganglia corresponds in the main with 

 that seen in /A//'./, but it should be noticed that at the end 

 of one of the terminal branohefl of the pallia! nerve given 



