2 Mr. A. Hancock on the Nervous System 



On laying open the ventral region of the head of Ommastrephes 

 todarus, the suboesophageal ganglions were soon ascertained to 

 hold their normal position. In this Cephalopod, however, they 

 are divided into three masses, one being placed a little in advance 

 of the other two ; but all above the alimentary tube. The an- 

 terior (PI. I. figs. 1, 2, 3 fl) is a depressed, irregularly circular 

 mass, giving off from the anterior border, on each side of the 

 median line, five large nerves (o, o) to the arms, and from the 

 posterior margin on each side two small ones {t, t), which were 

 lost in the muscular mass in front of the eyes. A commissure (c) 

 running backwards connects this with the second or median 

 mass, and is a very thick cord composed of numerous stout fila- 

 ments, most of which pass over the ventral surface of the anterior 

 ganglion, and becoming united to the brachial nerves accompany 

 them into the arms. Thus each arm receives a nerve from the 

 median as well as from the anterior masses. A central filament 

 was lost in the substance of the anterior mass. 



As soon as the brachial nerves enter the root of the arms 

 they swell out a little, each forming an indistinct oval ganglion 

 (fig. 2, Sp,p); these ganglions are united with each other by 

 nervous cords, and thus a complete chain of nerves and gan- 

 glions encircles the oral channel. The brachial nerves {o', o') are 

 continued on from the ganglions to the extremity of the arms 

 within a central channel, giving off filaments on either side, 

 several of which pass through the substance of the organ and go 

 to the skin. The surface being thus co])iously supplied with 

 nerves is probably highly sensitive. Filaments are given off 

 from the ganglionic chain at the base of the arms ; these fila- 

 ments pass inwards and enter the muscular bands that tie the 

 oral lamina to the arms. This lamina arises from the wall of the 

 oral channel, and advancing embraces the fleshy fringe which 

 immediately surrounds the beaks ; it is then turned back upon 

 itself, and forms a broadish scalloped membrane having points 

 or rays which are rather thick and fleshy. These rays corre- 

 spond to the muscular ties ; and on the nervous filaments from 

 the ganglionic chain entering the bases of the rays, they become 

 united to elliptical ganglions {q, q), from which the nerves {q', q') 

 much enlarged are continued to the extreme points of the rays. 

 These ganglions and nerves distribute numerous filaments which 

 ramify over the oral membrane ; the branches are most plentiful 

 towards the points of the rays. This membrane, which corre- 

 sponds very well with the external and internal labial processes 

 in Nautilus, is probably an organ of taste, the sense being more 

 particularly located in the points or rays ; it is moreover supplied 

 with numerous large oval follicles, mostly associated in pairs, and 

 having one of their extremities opening by several pores on the 



1 



