of Ommastrephes todarus. 3 



surface ; these are probably for the purpose of secreting sahva or 

 mucus. 



The median mass (PL I. figs. 1, 2, 3 i) is somewhat depressed, 

 long, narrow, and divided by a median depression in the longi- 

 tudinal direction. At the upper surface two large nerves {%) are 

 given off to the funnel ; these nerves spread out in the substance 

 of that organ in a radiating manner. Immediately behind the 

 origin of the funnel nerves the auditory nerves {j) come off; 

 each of these is short and passes at once to the auditory sac, 

 which is protected within a cavity in the cartilaginous cranium. 

 The sac completely fills the cavity, and has the inner surface 

 studded with a few tubercles apparently of soft pulpy matter. 

 The minute calcareous otolithe (PI. II. fig. 4), which also ad- 

 heres to the inner surface of the sac, is depressed, rounded, and 

 enlarged at one end, and produced into a slightly curved point 

 at the other. The median mass gives off from the anterior 

 margin the great commissure (c) that connects it to the an- 

 terior mass, and is united above to a broad nervous collar which 

 closely embraces the oesophagus. On the opposite side of the 

 collar, above the alimentary tube, are developed the optic gan- 

 glions (PI. I. fig. 3 /, & PI. II. figs. 1, 2, 3 I) ; they are fused into 

 one, rounded and prominent behind, and produced into an obtuse 

 point before ; a slight depression sufficiently indicates its bilateral 

 formation. Each half gives off from its outer margin a large, 

 broad, depressed nerve (PI. I. figs. 2, 3 A;, & PI. II. figs. 1, 2, Sj), 

 which, as it approaches the posterior wall of the eye, is sur- 

 rounded by a thick fold (PI. II. figs. 1, 2 k) of ganglionic matter ; 

 this fold, as well as the nerve, is striated ; the former breaks up 

 into numerous filaments (PL II. fig. 3 n, n), which, spreading 

 over the back of the eye-ball, supply the retina. The optic gan- 

 glions are also directly connected with the median nervous mass, 

 as can be seen by laying open the oesophageal collar, and removing 

 the membrane or sheath. Thus we find that the anterior and 

 median are in connexion with all the organs of the senses that 

 have yet been clearly determined in these animals, and the curious 

 mode in which they give off the brachial nerves would seem to 

 prove that they form but one centre. If this be doubted, how- 

 ever, it is only necessary to refer to other species to show that 

 such is really the case. 



In Cuvier's memoir on the Cephalopods it is stated, and the 

 parts are figured, that the nerves of the arms, funnel, and audi- 

 tory organs are all supplied by a single pair of large ganglions, 

 which by commissures are brought into connexion with the optic 

 centres, evidently much in the same manner as in Ommastrephes. 

 And Professor Owen has shown that in the Pearly Nautilus the 

 arms or tentacles, and funnel, derive their nerves from a single 



1* 



