POLYGYRA ALBOLABRIS AND LIMAX MAXIMUS 269 



the buccal body, but varying somewhat in position according to 

 the degree of contraction of the body. 



The infra-esophageal ganglia are situated below and just pos- 

 terior to the buccal body, and are connected with the supra- 

 esophageal ganglia by a double commissure. The buccal ganglia 

 consist of two small masses, situated just below the surface of 

 the posterior dorsal part of the buccal body. They are connected 

 with each other and with the supra-esophageal ganglia. 



The esophageal ganglia and the connecting commissures are 

 enveloped by an essentially opaque sheath, and it requires very 

 careful manipulation to remove this so as to determine the form 

 of the ganglia. This is best effected by two small needles fixed in 

 the end of small round sticks, as described on page 241, using 

 one in each hand. The points of the needles should be inserted 

 just below the surface of the sheath, and a little of it torn away 

 with each insertion, being very careful not to introduce the needle 

 far enough to penetrate the ganglia beneath. The fine forceps, 

 mentioned on page 241, will be found useful in removing the 

 loosened parts of the sheath. In this operation it is necessary to 

 proceed very slowly. Any undue haste will almost certainly 

 result in the destruction of the ganglia. 



The supra-esophageal ganglionic mass, before the removal of 

 the sheath, has the appearance of a single quadrangular mass, 

 wider than, long, the posterior margin incurved. The double com- 

 missures proceeding from the posterolateral extremities, appear 

 as single large, flattened nerves. When the sheath is removed, 

 the supra-esophageal ganglionic mass is seen to be composed 

 of two sets of ganglia, connected by a commissural cord, the 

 ganglia of each set being aggregated together, the two ganglionic 

 masses being precisely similar in detail. The principal one of the 

 supra-esophageal ganglia (pi. 12, a) is subquadrangular or sub- 

 ovate in outline, about two and one half times as long as wide, 

 slightly constricted at the middle. Attached to the lower outer 

 part of this ganglion is a smaller ganglion, about one fourth the 

 size of the preceding One. Attached to the posterior part of these 

 ganglia are three comparatively small, nearly round ganglia (pi. 



