20 THE VOYAGE OF H.M.S. CHALLENGER. 



this white portion, to the left, lay the branchia, with the small kidney at its posterior left 

 end, while in front, more to the left, the olfactory organ was situated, and at the posterior 

 extremity of the latter, the pericardium. Near the hinder end of the mucus and albumen 

 gland, the larger, right, triangular, shell-muscle facette arose (fig. 8, c) ; the left facette, 

 which was longer, narrower, and on the whole smaller, lay on the left side of the anterior 

 margin of the pericardium and posterior end of the olfactory organ. On the under side 

 of the last turn of the shell, on the right, lay the ovary. Shining through, on the left 

 side of this turn, the stomach could be seen for a short distance, of a grey colour, but 

 elsewhere covered by the whitish liver. 



The bulbus pharyngeus, the more distinct radula sheath, and the foliated stomach, were 

 seen shining through the floor of the branchial cavity, and all exhibited the normal relations. 



The central nervous system was in essential agreement with that of the typical 

 Marsenice. The arrangement of the ganglia was perfectly typical. Of the two cerebral 

 ganglia, which lay anteriorly (fig. 10, a), the left was smaller than the right and less 

 markedly separated from the pleural. The two pleural ganglia, which (fig. 10, b, b) lay 

 behind the cerebral, were almost as large as the latter, and again the left was somewhat 

 smaller than the right. The supra-intestinal ganglion, situated above the left cerebro- 

 pleural mass, had (fig. 10, d) a long oval form, and was united by a very short connective 

 with the left pleural, and by a long connective with the right (fig. 10). The infra- 

 intestinal ganglion (fig. 10, c), was as usual compressed, had a somewhat bent form, and 

 was superiorly connected with the right pleural by a short band, while inwards (to the 

 left) it was united to the left pleural by a long connective. The pedal ganglia (fig. 11) 

 lay beneath the others, and were almost entirely enveloped by a continuation of the 

 white glandular layer covering the foliated stomach. They approached one another in 

 the middle line, and each was short and irregularly pear-shaped, with the tubercle-like 

 process (fig. 11, a, a) at the anterior end. The right pedal was connected as by a short pro- 

 cess with the right cerebro-pleural mass, while the other was united to the left mass by two 

 longer, separate, cerebro- and pleuro-pedal connectives (fig. 11, b, b). The buccal ganglia 

 (fig. 10, e) were plano-convex, and were about a third the size of the cerebral. They 

 were united by a commissure which was about twice as long as the diameter of the 

 ganglia. The nerves seemed to originate in the same way as in the typical Marsenice. 



The eyes appeared as in the Marsenice (fig. 9), and two white calcareous points visible 

 below the pedal ganglia and embedded in the pedal musculature represented the usual 

 otocysts (fig. 11, c, c). They measured about 0'24 mm. in diameter, and the dull calcareous, 

 spherical otolith about - l mm. The auditory vesicles seemed to be connected by a fine 

 nerve with the external inferior portion of the relative pedal ganglion. The feather-like 

 olfactory organ exhibited a structure exactly like that of the Marsenice proper, and was 

 provided on each side with thirty-five leaflets. 



The external mouth (fig. 9) lay further forward on the under side of the head than in the 



