712 



ZOOLOGY 



SECT. 



and the pigment becomes more widely diffused. When the fibres 

 are relaxed the elasticity of the wall comes into play, and the 

 chromatophore contracts, the contained pigment thus assuming a 

 more condensed form. A peculiar iridescence which, in addition 

 to, the play of colours, is recognisable in the integument of Sepia, 

 is due to the presence of a number of cells, the iridocysts. 



When the mantle -cavity is laid open (Fig. 621) there is seen 

 on each side of it one of the two plume-shaped ctcnidia (cten.). 



In the middle line of the posterior 

 surface, close to the internal open- 

 ing of the funnel, is the anal aper- 

 ture (an.), situated at the oral ex- 

 tremity of a longitudinal tube 

 the rectum. On either side of 

 the rectum is a much narrower 

 projecting tube with a terminal 

 opening the nepliridial aperture 

 (neph.). On the left-hand side is 

 the opening of the spermiduct or 

 oviduct (ovid.) as the case may be. 

 In addition to the shell, which 

 is an important protective struc- 

 ture, and gives support to the 

 muscles of the fins, Sepia also has 

 a remarkably well developed in- 

 ternal skeleton composed of cartilage. An important part of 

 this the cranial cartilage (Fig. 619) protects the principal 

 nerve centres, encloses the auditory organ, and gives support 

 to the eyes. Other cartilages support the bases of the arms. 

 A thin shield-shaped plate the nuchal cartilage (Fig. 620) 

 lies on the posterior surface of the neck. The 

 pair of elevations on the posterior wall of the 

 funnel and the corresponding depressions on the 

 anterior surface of the body are borne each on 

 a thin plate of cartilage, and thin cartilages 

 support the bases of the fins. 



Alimentary System. The mouth is sur- 

 rounded by a thin peristcmial membrane, within 

 which is a circular lip beset with numerous 

 minute elevations. Lodged within the circular 

 lip is a pair of powerful horny jaws (Fig. 622, 

 Fig. 62B 9 jaw l ,jaw*- 9 Fig. 624, /.; Fig. 626, ya 

 somewhat the ,appearance of the jaws of a parrot, with one, 

 the posterior, larger and more strongly bent than the other, 

 which it partly encloses. The mouth leads into a thick- wall< 

 buccal cavity, which contains an odontophore bearing numerous 

 minute horny teeth. The oesophagus (Figs. 623 and 624, ce. 



FIG. 619. Sepia cultrata, cranial car- 

 tilage seen from the posterior aspect, 

 the cavities of the otocysts exposed. 

 eye, position of eye indicated by dotted 

 line ; ot. otocyst ; pall. n. pallia! nerve ; 

 vise. n. visceral nerves. 



Fir;. (i20. Sepi< 

 cultrata, nuch; 



cartilage. 



These hav( 



