298 



THE CEPHALOPODA 



Loligo, Sepia, etc., there are elongated cartilaginous lamellae at the 

 bases of the fins. There is a nuchal cartilage at the base of the 

 neck of all the Dibranchia in which the mantle is not fused to the 

 head ; consequently this cartilage is absent in Sepiola and the 

 Octopoda (Fig. 264, D). It serves for the insertion of the lateral 

 muscles of the funnel. Cartilaginous pieces also occur at the 

 internal extremities of the retractor muscles of the head and funnel, 

 and even in the two branchial laminae (Sepia). In the Decapoda 

 there is sometimes a T-shaped basi-brachial cartilage at the bases 

 of the arms on the anterior (dorsal) side of the head (Sepia, 

 Fig. 264, C) ; it is united to the cranial cartilage and serves for the 

 insertion of the brachial muscles. Finally, the " resisting apparatus " 



FIG. 264. 



Cartilaginous skeleton of Cephalopoda. -4, capito-peclal cartilage of Xautilus, ventral aspect, 

 a, ridge which supports the pedal portion of the nerve-centre. B, right-side view of the same ; 

 the large anterior processes are sunk in the muscular substance of the funnel. C, cephalic 

 cartilages of Septa officinalis. D, nuchal cartilage of Sepia officinalis. (From Lankester, after 

 Refers tein.) 



mentioned above is formed by sub-epithelial cartilaginous projections 

 and depressions. 



It has been shown that Lepidoteuthis, a form not yet sufficiently 

 well known, but apparently a member of the Oigopsida, is ex- 

 ceptional in that the superficial portion of the integument gives 

 rise to a layer of hard, projecting, regularly disposed, imbricated 

 scales, lying above the chromatophores. In Octopus arborescens 

 there are ramified and contractile tegumentary papillae. 



In several Dibranchia the integument contains certain so-called 

 " aquiferous " cavities, which open to the exterior by special pores, 

 but have no communication Avith the circulate^ system. In 

 addition to the pockets of the tentacular arms of Decapoda, there 

 are cephalic pores on the back of the head and at the base of the 

 funnel in Ocythoe, and buccal pouches on the ventral side of the 



