72 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



it is so short that the two sets of ganglia form a close ring around the 

 anterior part of the buccal body. 



The third set of ganglia are the stomato-gastric, consisting of two 

 minute lateral masses, united by a short transverse commissure, and 

 always placed upon the buccal body immediately postero-laterally to 

 the commencement of the oesophagus. The stomato-gastric ganglia are 

 connected with the supra-cesophageal on each side, by means of a long, 

 delicate commissure, which is more or less loose, and permits a free 

 movement of the former ganglia with the buccal body to which they 

 are fixed. 



From the supra-oosophageal ganglia pass off on each side, — 1st, a 

 minute branch along the coarse of the supra-sub-cesophageal commis- 

 sure ; 2d, three or four small branches to the retractor muscles of the 

 eye-peduncles ; 3d, a large branch, the superior tentacular nerve ; 4th, 

 one or two small branches to the base of the eye-peduncle, for its integ- 

 ument ; 5th, the inferior tentacular nerve ; Gth, small branches to the 

 integument of the lips. 



From the sub-oesophageal ganglia pass off, — 1st, numerous branches 

 on each side, to the podal disk, and laterally to the integument ; 2d, a 

 branch on the right side to the penis; 3d, a branch to the vas deferens and 

 prostate gland ; 4th, on each side a branch to the retractor muscle of 

 the buccal body ; 5th, a large one to each s ir le of the collar and pulmo- 

 nary chamber ; 6th, a branch which follows the posterior aortic vessel, 

 which gives off branches to the muscular peritoneum ; 7th, branches to 

 the origin of the tentacular retractors ; 8th, branches to the oviduct, 

 ovary, testicle, stomach, intestine, and liver. 



From the stomato-gastric ganglia pass off on each side, — 1st, a 

 nerve to the external muscular structure of the buccal body ; 2d, two 

 branches which penetrate posteriorly into the buccal body ; 3d, a branch 

 to the salivary duct and gland ; 4th, a branch to the oesophagus and 

 stomach ; 5th, branch to the interior of the buccal body anteriorly. 



The above distribution of the nerves has been principally derived 

 from dissections of Glandina and Mesodon albolabris. In the former 

 genus, upon what is the nerve to the tentacle in the other genera, there 

 is formed, near the base of the eye-peduncles, a ganglionary enlargement, 

 from which passes off the true, inferior tentacular nerve of this animal, 

 and two other large branches to the third, or external tentacle. 



The nervous centres are composed of ganglion globules, varying very 

 much in size ; some are very large, others are not more than one eighth 



