H. B. Krrx.—On the Anatomy of Sepioteuthis bilineata. 149 
such cases the chromatophores are well-defined; but often the outline is 
very ill-defined in one direction. This may, however, be due to the 
coloured contents having flowed out, leaving a part of the capsule empty, 
its thin walls being often invisible from their transparency. 
The chromatophores appear to be in two distinct layers, as at times one 
may be seen distinctly overlying another. Thus a deep brown chroma- 
tophore may be seen over a yellow one; pink may be seen over yellow ; 
chocolate-brown over pink, and so on. 
Above the layer or layers containing the chromatophores is a colourless 
cuticular layer ; below it is a layer containing muscular fibres. 
The whole integument is very loosely attached by fine muscular fibres 
to the substance of the animal; it is loose, but nowhere wrinkled, and is 
very elastic. 
Cartilages. 
The cartilages are—the cephalic cartilage, the neck cartilage, the hinge 
and articular cartilages, and the pinnal cartilages. 
Cephalic cartilage (pl. viii., fig. 2).—The cephalic cartilage forms, when 
the animal is in a walking position, a roof for the eye-balls.. An idea of its 
general shape may perhaps be best obtained by imagining a broadly cordate 
leaf with its apex and the base of the midrib infolded towards the centre. 
The posterior side shows a marked depression, and the outline is here 
strongly concave. From within the central point of the posterior margin 
rises a slight prominence, which gives off two small wing-like cartilaginous 
expansions which lie upon the eye-ball. The anterior outline is concave, as 
are to some extent the lateral margins. The cartilage is pierced at its 
centre by the aperture for the gullet and visceral nerve branches. This 
aperture has its margin strengthened by a cartilaginous ridge on either side, 
the two ridges receding slightly from the aperture, but becoming confluent 
on the posterior aspect and rising to form the prominence already noted. 
In the cup formed by the receding of these ridges lies the peri-cesophageal 
nerve ring. On either side of the ridge formed by their confluence are two 
perforations. 
Neck cartilage (pl. viii., figs. 8, 4).—Lying on the neck is a cartilage of 
irregular diamond shape. Its sides are incurved, so as to give ib a spoon- 
shape. Attached to it, and passing upwards, is a double muscular band 
attached at its opposite extremity to a tough membrane which covers the 
gladius. Thus the neck of the animal is strongly attached to the anterior 
part of the mantle. The anterior aspect of the cartilage has a raised central 
ridge, grooved throughout its length. This ridge corresponds with the 
channel of the gladius. 
