170 BULLETIN OF THE 



The large ganglion cells of the third class (cl. gn. III.) are present in 

 a somewhat limited number, and always in a definite position. They lie 

 in the posterior third of the brain, on its medial posterior boundary 

 (Figs. 19, 20, 25). The large fibres which pass off from these cells are 

 easily seen to turn toward the opposite side of the body and to make 

 their way into the ventral commissure, where they are lost to view, 

 either because they are split up into a number of small ones, or from 

 some other cause suffer a diminution in diameter. This crossing of 

 fibres from cells on one side of the body to the connective ^ of the other 

 certainly does not take place frequently in either of the other two groups 

 of ganglionic cells. Wherever circumstances permitted the following of 

 nervous processes in groups I. and II., these were seen to pass off towards 

 the connective on the same side of the body as the cell itself. 



h. Cerebral Nerves. 



From either side of the brain two groups of nerves pass off; the an- 

 terior consists simply of the first tentacular nerve (ii. ta. 1, Fig. 22, 

 Plate II.) ; the posterior contains the second, third, and fourth tentac- 

 ular nerves and the oesophageal connective. The tentacular nerves 

 I'adiate from the brain to the aboral wall of the tentacular fold, and, 

 splitting there into numerous branches, follow the aboral wall of the blood 

 cavity toward the distal margin of the fold. The first tentacular nerve 

 supplies that portion which was designated as the dorsal horn. Follow- 

 ing the margin of the fold from this region toward the ventral line, its 

 successive parts are seen to receive their nerve supply from the third, 

 second, and fourth tentacular nerves successively. Each of these in- 

 nervates about equal portions of the fold. I was unable to trace the 

 ultimate termination of the nerves in this region. 



The oesophageal connectives give off each three branches : (1) the 

 splanchnic, (2) the muscular, and (3) the inferior muscular. The 

 splanchnic is given off ventrally and medially immediately after the 

 connective leaves the ganglion (n. spl, Figs. 22, 25). It passes diag- 

 onally forward, — not posteriad,^ as stated by other writers,^ — and into 



1 I use tlie word cojinective in the sense first suggested by Lacaze-Duthiers, to 

 distinguish the nerve fibres joining ganglionic nerve centres whicli are on the same 

 side of the body, reserving the word commissure for such fibres as cross tlie median 

 plane of the body. 



2 This nerve is turned backward in Figure 22, for the sake of clearness in the 

 drawing. Normally, it extends forward under the ganglion. 



3 This relation is obscured when the introvert is slightly retracted, and even 

 apparently reversed when the retraction is greater. 



