6 MR MACDONALD ON THE ANATOMY 



curved meniscus, in which a cell-structure is often distinctly visible beneath the 

 cutaneous covering. 



The acoustic capsules (Plate I. fig. 1, c, fig. 2, m) contain each a transparent glo- 

 bular otolith, which is very much smaller than the lens of the eye. Several little 

 prominences, on the inner surface of the capsules, represent those which poise off 

 the crucial otolith of Sepia, from the wall of the vestibule in which it lies. The 

 ear-sacs, moreover, appear to float freely within the muscular sheath, being 

 connected with the cerebroid ganglia by long and delicate auditory nerves. 



The nervous system of this creature, from the peculiar mode of distribution of 

 its ganglia and communicating or commissural cords, not a little resembles the 

 Ao/wo-gangliate type. 



Two elliptical knots of nervous matter lying side l)_yside, and blended together by 

 theircontiguous borders, compose the cerebroid ganglia (Plate I. fig. 2,i) in which the 

 combination of several smaller centres maybe distinctly traced in recent specimens. 



Two large nerve-trunks, derived from the cerebroid ganglia anteriorly, com- 

 municate with the before-mentioned buccal ganglia, lying at the posterior extremity 

 of the lingual cartilages, and give off nerves to the buccal mass and mouth. 



The optic nerves i^Plate I. fig. 2, h) emerge from the posterior part of the outer 

 border of the cerebroid ganglia, by a clul)-shaped base, and taper gracefull}' 

 towards the eyes, at the back part of which they form a remarkably thick retinal 

 expansion. 



The delicate auditory nerves arise immediately behind the optic, and thence 

 passing outwards and backwards some little distance, reach the acoustic sacs (Plate 

 I, fig. 1, c, fig. 2, m), upon the walls of which other more delicate filaments are also 

 distributed. On examining the origin of the larger nerves, it would appear as 

 though they communicated with each other in the median line by very faint striae 

 traversing the substance of the cerebroid ganglia. From the posterior border of the 

 latter bodies, two large nervous chords (Plate I. fig. 2, n) pass directly backwards, 

 including between them the oesophagus (Plate I. fig. 1, e, fig. 2,g) and buccal artery 

 (Plate 1. fig. 2, e), and having reached the root of the swimming-fin, theyjoin the 

 fore part of the pedal ganglia (Plate I. fig. 1, h, fig. 3, a) — two nearly circular but 

 laterally compressed masses of nervous matter connected with one another by 

 their contiguous surfaces. 



These ganglia give off numerous branches to the neighbouring parts, but from 

 the inferior border of each a special nerve descends wdth the pedal artery, and 

 is ultimately distributed to the swimming-plate, while two stout trunks, arising 

 from the posterior part of the ganglia, blend together in a loose plexiform manner, 

 and course backwards as a single chord. This at first accompanies the oesophagus, 

 to which it supplies several branches, next sends off a nerve of communication to 

 the visceral ganglia, and, finally subdividing in the tail, is lost in the filamentous 

 appendage. 



