542 



CEPHALOPODA. 



on each side : these sinuses are relatively larger 

 in the Sepia than the Octopus. In both species 

 the branchial vein resumes its ordinary dimen- 

 sions before terminating in the ventricle; but in 

 the Cuttlefish the sinus is placed closer to the 

 ventricle. 



The systemic ventricle (o) is situated in the 

 mesial plane between the bifurcation of the 

 vena cava above, and the ovary or testis below. 

 In the Octopus and Eledone it presents a glo- 

 bular form, rather extended tranversely, and 

 with the branchial sinus entering at its superior 

 and lateral aspects. In the Loligo and the 

 Onychoteuthis (fig. 227) it is lozenge-shaped, 

 witii the long axis in the axis of the body ; 

 giving off the two aortse (c, d) by the anterior 

 and posterior angles, and receiving the bran- 

 chial veins (a, a,) at the lateral angles. In the 

 Sepia, (o, Jig. 225,) Sepioteuthis, and Rossia, 

 the systemic ventricle is a fusiform body, bent 

 upon itself at right angles. About one-half on 

 the right side lies in the axis of the body, the 

 remainder extends transversely to the left side ; 

 the extremity of this part receives the left bran- 

 chial vein, the other extremity gives off the an- 

 terior aorta (q, jig, 225). The bulb of the 

 posterior and generally the larger aorta (p, Jig. 

 225) is continued from the middle of the 

 transverse portion ; the right branchial vein 

 enters the middle of the right side of the lon- 

 gitudinal portion of the ventricle. 



In all the Dibranclilata the parietes of the 

 systemic heart, though thin, are firmer and more 

 muscular than those of the branchial hearts; and 

 its cavity is generally about three times greater 

 than that of either of the others : its inner 

 surface shows the regular interlacement and 

 decussation of the columnar carneae, none 

 of which, however, project into the cavity. 

 The termination of each branchial vein is 

 defended by a pair of membranous semi- 

 lunar valves (b, Jig. 227). The origin of the 

 lesser aorta (p), arising from the anterior part 

 of the ventricle, is defended by a single valve 

 (e,Jig. 227); that of the great aorta, (o',fig. 

 226,) which, though posterior in its origin, is de- 

 stined to supply the head and anterior parts of 

 the body, is generally provided with a mus- 

 cular bulb, as in the Nautilus, in the Octopus 

 it is defended, according to Cuvier, by two 

 semilunar valves ; but in the Calamary and 

 Onychoteuthis by a single valve (f, Jig. 227). 

 In the Octopus there is also a third small 

 artery (r, Jig. 225) given off directly from the 

 ventricle, which is distributed to the generative 

 organs, and presents considerable periodical 

 variations of size in relation to the functions 

 of those parts. In the same genus the small 

 aorta, which arises from the anterior part of 

 the ventricle, first gives off two long and slender 

 branches (s, s, Jig. 226), which are distributed 

 to the venous follicles, whose arterial vascularity 

 we have before mentioned. The trunk then di- 

 vides into two arteries, of which the largest (t) 

 ascends in front of the vena cava to be distri- 

 buted to the mantle; the other supplies the 

 folded intestine and surrounding peritoneum. 

 The large aorta first passes backwards and to 

 the right between the layers of peritoneum 



which separate the intestinal sac from that of 

 the pyloric appendage and that of the stomach ; 

 winds round the latter, and passes, by a proper 

 opening, to the right of the cardia through the 

 muscular septum, and into the cavity behind 

 the liver, and ascends on the right side of the 

 dilated oesophagus to the cartilaginous cranium. 

 Here, after distributing branches to the sur- 

 rounding parts, it bifurcates and completely 

 encircles the gullet; and from this vascular 

 ring, which is strikingly analogous to the bran- 

 chial arches in Vertebrata, the head and all its 

 complex radiating appendages derive their nu- 

 triment. 



RESPIRATORY ORGANS. The branchiae pre- 

 sent the same general form and structure in both 

 orders of Cephalopods, but differ, as before ob- 

 served, in number, and also in their mode of 

 attachment to the mantle. They are always 

 entirely concealed and protected by the mantle, 

 which is extended forwards so as to form a 

 peculiar chamber for them anterior to the other 

 viscera, and into which the rectum and gene- 

 rative organs open. It is interesting to perceive 

 the respiratory cavity retaining, in the highest 

 organized Mollusks, that relation with the anal 

 extremity of the digestive canal which we trace 

 through the whole of this type of animal con- 

 formation, and which forms so well-marked a 

 line of distinction between the Molluscous and 

 Vertebrate divisions of the animal kingdom. 



In the Nautilus the four branchiae are at- 

 tached by their bases only to the inner surface of 

 the mantle; but in the Dibranchiates a thin 

 fibrous membrane connects the fleshy stem of 

 each gill to the contiguous surface of the man- 

 tle. In the Nautilus the branchiae are subject 

 to contortions from the want of this support ; 

 and in the specimen which we dissected, we 

 found the gills on one side closely bent upon 

 themselves, with their apices turned down; this 

 circumstance does not probably impede a cir- 

 culation which flows with an equable and con- 

 tinuous current through the gill ; but where the 

 blood is driven in jerks by the contractions of 

 a powerful ventricle, a necessity then exists for 

 the provision of a free channel for the passage of 

 the fluid ; and accordingly we find that the 

 obstruction of the branchial artery by the 

 bending of the fleshy stem of the gill is obvia- 

 ted by the simple but effectual means above 

 described, viz. the snperaddition of a connect- 

 ing membrane, which always preserves the gill 

 in a straight position. 



In both orders of Cephalopoda the branchiae 

 present an elongated pyramidal figure, with their 

 apices directed forwards : they are compressed 

 from before backwards in the Nautilus (n, m, 

 fig. 224), and from side to side in the Cuttle-fish 

 '(i, k, fig. 225) and most other Dibranchiates. 

 They are composed of a number of triangular 

 vascular laminae extendingtransversely from each 

 side of a central fleshy stem (h,fig. 225), having 

 an alternate disposition : each lamina is com- 

 posed of smaller transverse laminae, which are 

 again similarly subdivided ; the entire gill thus 

 exhibiting the structure called by botanists ' tri- 

 pinnate,' by which an extensive surface is afford- 

 ed for the minute division of the branchial vessels. 



