CEPHALOPODA. 



525 



Fig. 212. 



Skeleton of t/te Cuttle-fish. 



nous prominence arising from the inner sur- 

 face of the sides of the mantle. This pro- 

 minence in the Sepia is of an oval shape ; but 

 in the Tenthidte it forms a narrow, elongated, 

 cartilaginous ridge, and is adapted to a cor- 

 responding groove at the sides of the funnel. 

 In the Calamary the ridge is of the same size 

 with the groove ; but in the Onychoteuthis the 

 ridge or antero-lateral cartilage commences at 

 the anterior margin of the mantle, and extends 

 downwards some way below the termination of 

 the infundibular groove. Rathke* discovered 

 in the corresponding part of the mantle of the 



* Memoires de 1'Acad. Imp. des Sciences 

 Petersbourgh, torn. ii. pt. 1 et 2, p. 154. 



d 



Loligopsis, viz. on either side and towards 

 the ventral aspect, a thick, opaline, elongated 

 cartilage, extending longitudinally for more 

 than half the length of the mantle, and sup- 

 porting a series of wart-like processes. These 

 lateral tuberculated cartilages in Loligopsis we 

 regard as corresponding to the lateral ridges in 

 the Calamaries and Onychoteuthis above-men- 

 tioned ; but in the Loligopsis they are not arti- 

 culated with the sides of the funnel, which are 

 otherwise attached to the mantle. In all the 

 Decapods, however, this pair of cartilages on 

 the ventro-lateral aspects of the mantle is more 

 or less developed. 



In the Sepia a longitudinal cartilage is 

 situated on the ventral aspect of the liver. 

 The long lateral fins are, in the same genus, 

 each supported by a narrow, flattened, elon- 

 gated, cartilaginous plate (D, D, fg. 212 ) ; 

 pointed at its anterior extremity, obliquely 

 truncate behind ; smooth and gently concave 

 internally (g), but traversed by an irre- 

 gular longitudinal ridge (h) on its external 

 surface. These cartilages form the points of 

 attachment to the powerful muscles of the 

 lateral fins. From the dorsal ridge of each 

 cartilage a number of close-set fibro-cartila- 

 ginous laminae extend at right angles to the 

 cartilage to near the margin of the fin, with 

 their plane in the direction of the axis of the 

 body : they alternate with the strata of mus- 

 cular fibres, resembling the rays which support 

 the fins of fishes. 



The analogy of this structure to the cartila- 

 ginous basis of the great pectoral fin of the Ray 

 is so close and satisfactory that we can scarcely 

 hesitate to acknowledge the locomotive appen- 

 dages of the mantle in the Decapodous Cepha- 

 lopods as representatives of the pectoral fins of 

 fishes, and consequently of the anterior extre- 

 mity of the vertebrated animal. As they are 

 not, however, fixed to a vertebral column, their 

 situation is not constant, being sometimes, as 

 in Rossia, situated towards the anterior part of 

 the body; sometimes, as in Loligo, placed at 

 the posterior extremity; just as we perceive the 

 ventral fins of Fishes shifting their position, in 

 consequence of a similar want of connexion, 

 so as to occupy, in some species, a position 

 more anterior even than the pectoral fins, with- 

 out losing their essential character, as the ana- 

 logues of the posterior extremities. 



The cartilages of the fins correspond in length 

 to the parts which they support, and are con- 

 sequently much longer in the Cuttle-fish than 

 in the Calamaries; in the Octopods they are 

 entirely wanting. 



Locomotive System. The organs of loco- 

 motion in the Cephalopods are of two kinds, 

 one consisting of appendages developed from 

 the head ; the other of rudimental fin-like ex- 

 tremities developed from the trunk ; the latter 

 organs are confined, as we have seen, to the 

 Decapodous genera of the higher or Dibran- 

 chiate Order. 



The cephalic processes, which are called 

 digitations, arms, feet, tentacles, and pedun- 

 cles, have no real homology with the loco- 

 motive extremities of the Vcrtebrata ; to these 

 they are analogous only, inasmuch as they 



