M L L U S C A. 



607 



ears. These arc situated in the annular cartilage which 

 supports the arms. In this cartilage, there are two 

 cavities. In each of these, there is a bag rilled with 

 a gelatinous transparent fluid, and containing a calca- 

 reous substance, differing in its consistence, according 

 to the species, from the brittleness of starch to the 

 hardness of bone. 



The auditory nerve penetrates the walls of this laby- 

 rinth, and ramifies on the membranous bag which i 

 contains. There is no external opening, nor any ap- 

 parent alteration in the thickness of the investing in- 

 teguments. 



The digestive system of the cephalopoda exhibits 

 several appearances by which it may be distinguished. 

 The arms which surround the mouth, seize the animals 

 which are to serve a* food, and bring them to the 

 mouth. The mouth is situated in the centre of the 

 disk, round which the tentacula are arranged. It is 

 surrounded with a slight fold of the skin, which may 

 be compared to lips, and which is rough on the central 

 aspect. Within these are the two mandibles, of a deep 

 brown colour, hard horny consistence, and in form 

 resembling the beak* of a parrot. Where free, they 

 are conico-tobular, but where covered, they are open 

 at the central side. The under beak, unlike the same 

 organ in birds, is the largest, the most crooked, and 

 embraces the upper, or the one on the dorsal margin of 

 the mouth. These jaws are merely able to open and 

 shut, as they possess no lateral motion. They are sup- 

 ported by the muscular bed of the mouth, which serve* 

 a* mould to fill the cavity towards the point. The 

 tongue is situated between the beaks, and is armed 

 with reflected teeth. These teeth, in consequence of the 

 undulatory motion of the substance of the tongue, ex- 

 pedite the progress of the food into the gullet. 



The salivary glands are four in number j the first 

 pair, seated 'on each side the muscular bed of the 

 mouth, are each divided into numerous lobes, whose 

 mctetory duct* poor their fluid into the beginning of 

 the gullet. The second pair, seated lower down and 

 below the eye*, are not so much divided, and send out 

 each a canal. These unite, and pour their contents 

 into the mouth. 



The gullet is furnished with a lateral expansion, not 

 unlike the crop of gallinaceous birds. The stomach is 

 rawcnlar, like the gizzard of fowl*, and the cuticle is 

 thick, and separates easily from the other membranes. 

 At the pyloric opening of the stomach, there is another 

 aperture equally large, which leads into the spiral slu- 

 mack, or caecum, as it has been improperly termed by 

 some anatomists. It may with greater propriety be 

 denominated the duodenum, as it performs some of 

 the Mem of that part of the gut in the higher orders 

 of animal*. This stomach is conical, closed at the dis- 

 tal extremity, and performs about a turn and a half, 

 like a spiral shell. Its inner surface is covered with a 

 ridge, which traverses it in a clo&ely spiral direction. 

 The bile flow* into it near the apex, and towards- 

 its base glandular orifices pouring out a thick yellow 

 fluid may be observed. The intestine, after leaving 

 the pylons, in some species makes one or two turtu, m 

 others it proceeds directly to the anus. This opening 

 is seated at the base of the funnel, on its posterior or 



. 



The liver is of considerable size, of an orange-yellow 

 eolour, and of a soft and spongy texture. It gives rise 

 to two hepatic duets, which proceed to the extre- 

 mity of the spiral stomach, where they empty the 



orange-coloured bile which they contain by a common 

 orifice. " 



The organs of circulation consist merely of veins and 

 arteries, which we distinguish into pulmonic and sys- 

 temic. The veins which have their origin in the feet, 

 mouth, and annular cartilage, coalesce, and form two 

 branches, which afterwards unite into a common trunk. 

 This vessel, after descending through part of the vis- 

 cera into the abdomen, divides into two branches, each 

 of which may be considered as a vena cava, conveying 

 the blood to the lateral hearts. Each vena cava, at it* 

 origin, is joined by an equally large vessel, which emp- 

 ties its contents in a direction nearly at right angles 

 with the former. These veins arise in the stomach, 

 intestines, liver, and organs of generation. The vena 

 cava receives a second large vessel, nearly in the same 

 direction as the first, which has its origin in the tunic 

 and the supports of the branchiae. From the size of 

 the vena cava, in consequence of the union of these 

 two branches, and the appearance of muscular ridges 

 on its inner surface, it has been compared by some to 

 an auricle. 



On each side, in the common cavity of the tunic, 

 and near the gills, an aperture may be observed, the 

 entrance to a bag or cavity. Each cavity is traversed 

 by the vena cava of that side, and in its passage exhi- 

 bits a curious confirmation. The surface of the vein 

 is covered with spongy glandular bodies of different 

 shapes. These, upon being pressed, pour out an 

 opake yellow mucous fluid. Within, these glands 

 communicate by means of very wide ducts with the 

 cavity of the vein. Indeed, when air is blown into 

 the vein, it readily pastes through the glands into the 

 bag, and from thence into the cavity of the tunic ; and 

 when air is blown into the bag, it likewise penetrates 

 the gland, and passes through into the veins. The 

 arteries with which these glands are furnished are com- 

 paratively minute. 



It appears probable that these glands separate some 

 principle from the blood, and that this is conveyed 

 away by the ejection of the water from these venous 

 bags into the common cavity. Were it practicable to 

 analyse the yellow mucus which these glands contain, 

 some light might be thrown on the subject. Indeed, 

 it appears not improbable that this arrangement is ana- 

 logous in its functions to the urinary system in ths 

 moat perfect classes. 



Each vena cava enters its corresponding lateral heart 

 or ventricle, through an intervening valve. Each late- 

 ral heart is situated at the base of each gill, is pear- 

 shaped, black, moderately thick, with numerous pits 

 on its inner surface. Its narrow end terminates without 

 any valvular structure in the pulmonary artery. In the 

 genus octopus, the lateral hearts are naked ; but in the 

 generalolego and sepia, there is suspended from each, by 

 a slender footstalk, a spongy round body, which is con- 

 cave beneath. The footstalk consists of fibres, which 

 are attached to the surface of the heart, but there is no 

 communication by ducts or vessels. The use of thi* 

 organ is unknown. 



The animals of this class continually reside in the 

 water, and respire by means of gills or branchiae. 

 These are double, one on each side corresponding with 

 the lateral pulmonic ventricles. Each gill is connected 

 at its opposite sides to the tunic, by means of fleshy 

 ligamentou* bands. Between these, the double leaves 

 of the gills are arranged in an alternate series. Each 

 leaf is supported by a footstalk from the band, and i* 



