54 



ORGANS OF SUPPORT, 



These compressed layers are connected together by in- 

 numerable, very mimits tubular fibres ; so that there is 

 a great analogy between the structure of this internal 

 laminated shell, and the external polythalamous shells, 

 where the successive laminae are more detached. In the 

 figure of the sepia (Fig. 25. 1,) the mantle has been cut 

 open at (,) to show the position and the successive lay- 

 ers of the shell. The lateral muscular fins (#,) by which 

 the animal swims, extend along the whole sides of the 

 abdomen, the funnel (c,) for the passage of all the ex- 

 cretions, extends from the anterior part of the open 

 sac. In the centre of the arms or feet, radiating from 

 the head, is placed the mouth (d,) provided with two 

 dense and sharp mandibles, and the two long muscular 

 tentacula (e,) extend from the fore part of the head (/,) 

 between the first and second pairs of feet* In many of 

 the naked cephalopods the dorsal shell contained within 

 the substance of the mantle is destitute of calcareous 

 matter, and reduced to a mere thin, flexible, transpa- 

 rent, cartilagenous lamina, as we find in the loligo, the 

 sepiola, the loligopsis, and others. These uncalcified shells 

 are contained in a dorsal sac of the mantle, like the cal- 

 careous laminated shell of the sepia. The position of 

 the thin, stiliform, cartilaginous lamina in the lack of the 

 sepiola vulgaris, is seen in (Fig. 26. 1. ,) where the co- 

 loured covering and skin have been removed to show 

 the situation of the hard 



parts and the superficial FIG 2e - 



muscles. The dorsal la- 

 mina (,) is here very 

 small, flexible and short 

 from the great mobility 

 of the muscular part, 

 which forms its sheath. 

 In the loligopsis guttata, 

 the dorsal lamina (Fig. 



26. 2,) extends the whole length of the back of the man- 

 tle to the point of the tail, being spear-shaped, with very 

 thin flexible edges, especially at its broadest middle part. 

 That of the loligo sagittata, (Fig. 26. 3,) is more broad 

 and leaf-shaped, and extends, as most of the other soft, 



