H. B. Kirk. — 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 (pi. 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 bere 

 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-oesophageal 

 nerve ring. On either side of the ridge formed by their confluence are two 

 perforations. 



Neck cartilage (pi. viii., figs. 3, 4).— Lying on the neck is a cartilage of 

 irregular diamond shape. Its sides are incurved, so as to give it 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. 



