TETHYS DACTYLOMELA (RANG) 31 



107 of his Monografia, but the notation of his fig. 9, tav. IV does 

 not follow the same, nor is there any reference made to the figure 

 in the description. 



The first nerve is a strong, unpaired, median one arising 

 upon the dorsal, median region of the group by the union of a 

 large bundle of fibres from each ganglion (PI. Ill, fig. n, /). It 

 almost immediately bifurcates into two equal subdivisions which 

 pass directly into the pharyngeal bulb, and are distributed to the 

 muscles of the rotella, bearing the radula. 



The second nerve (PI. Ill, figs. 9, 10, n, 2), arises antero- 

 laterally and courses around the external face of the pharyngeal 

 bulb to the attachment of the lateral M. retractor bulbi. Here 

 it divides into two branches, the posterior one passing directly 

 inward, ramifies among the deep muscles of the radula, while 

 the anterior branch courses forward and is distributed to the M. 

 ant. lateralis bulbi, and to the deeper muscles of the bulb. 



The third nerve (PI. Ill, figs. 9, 10, n, j), arises close above 

 the base of the second nerve and passes around the side of the 

 bulb above and diverging slightly from it. At the posterior 

 border of the M. antero-lateralis bulbi it forks and passes beneath 

 that muscle, giving off branches to it as it passes deeper into the 

 bulb. It may be traced fonvard to the anterior end of the 

 bulb, where its delicate branches are finally lost among the deeper, 

 circular muscle fibres. 



The fourth nerve (PI. Ill, figs. 9, 10, n, 4) arises from the 

 lateral margin of the ganglion, behind and above the origin of 

 the third, and passes upward over the postero-dorsal face of the 

 pharyngeal bulb, following closely the external border of the 

 proximal portion of the salivary gland to the appearance of its 

 duct at the surface of the bulb. Near this point it penetrates 

 the outer layers of the muscular wall, and passes forward in it to 

 the anterior end of the bulb, giving off numerous branches to 

 the muscles of the dorsal portion. 



The fifth nerve (PI. Ill, figs. 9, 10, n, 5) is quite small, and 

 may be readily overlooked, or considered as a branch of the 

 sixth one. It arises close to the base of the latter, between it and 

 the fourth, and, on the left side, seems indeed to be a basal 

 branch of the sixth in many cases (PI. Ill, fig. 10, 5). On the 

 right side, however, it is distinct in origin. It is probably to be 



