608 



M O L L U S C A. 



subdivided into smaller leaves, to expose a greater sur- 

 face to the water. 



The pulmonary artery passes along this band, sends 

 a branch into each footstalk, which, penetrating the 

 substance of the gills, conveys the blood to its different 

 divisions. 



The systemic veins depart from the gills at the op- 

 posite extremity. These unite at the inferior band, 

 and from each gill a vessel proceeds to the single cen- 

 tral or systemic heart or ventricle. In some of the 

 animals of this class the systemic veins are somewhat 

 enlarged, and assume the appearance of auricles. The 

 two pulmonary, or rather the systemic veins, enter the 

 heart at the opposite side, each at the termination 

 being furnished with a valvular organization. 



The systemic heart is white and fleshy, and differs 

 according to the genera in its form, being in the Oc- 

 topus semicircular, but in the Loligo and Sepia lobed. 

 Besides giving rise to a large aorta, or principal arte- 

 ry, two smaller ones likewise proceed from its cavity. 

 These arteries are furnished at their entrance with 

 valves. 



The sexes in the Cephalopoda are distinct, the male 

 and female organs being found on different individuals. 

 There is not, however, any external mark by which 

 they may be distinguished. M. Cuvier found that the 

 n-.ales of the octopus were scarcely a fifth part so nu- 

 merous as the females. 



The male organs of generation consist of the follow- 

 ing parts. The testicle is a large white glandular purse, 

 containing numerous fringed filaments, from which the 

 seminal fluid is secreted. This fluid passes out of the 

 testicle, by a valvular opening, into the vas deferens. 

 This canal is slender, and greatly twisted in its course, 

 and opens into a cavity which has been compared to 

 the seminal vesicle. The walls of this last cavity are 

 strong and muscular, and disposed in ridges. Near 

 the opening at the distal extremity of this sac is an 

 aperture leading into an oblong glandular body, re- 

 garded as exercising the functions of a prostate gland. 

 Beyond this lies a muscular sac, divided at the top, 

 where it opens by two ducts, but connected at the base. 

 In this sac are numerous white thread-like bodies ter- 

 minated by a filament, but unconnected with the sac. 

 In the interior they consist of a spiral body, connected 

 at each extremity with a glandular substance. When 

 these bodies are put into water, they twist themselves 

 in various directions, and throw out at one of their 

 extremities an opake fluid. These motions are not ex- 

 cited by placing them in oil or spirit of wine, but they 

 may be exhibited by immersing in water those which 

 have been kept for years in spirits. 



These bodies, first observed by Swammerdam, and 

 afterwards by Needham, have been regarded by some 

 as demonstrating the truth of the vermicular theory 

 of generation j by others, they have been consider- 

 ed as analogous to the pollen of plants that their 

 tunic is in part soluble in water, and when they are 

 thrown into that fluid, they speedily burst, and spread 

 their impregnating contents over the eggs of the fe- 

 male. Although this last conjecture is plausible, and 

 countenanced by the circumstance that these vermi- 

 cular bodies are only found at the season of reproduc- 

 tion, the subject is still involved in obscurity. Are 

 these bodies produced in the testicle, and only brought 

 to this bag when nearly ready for exclusion ; or, if the 

 product of the bag itself, by what means are they nou- 

 rished ? 



The male organs terminate in a cylindrical fleshy 



body termed the penis. This is hollow within, and Moliusca. 

 ribbed with muscular bands. Near its base it receives '*~~~Y~~' 

 one of the ducts of the vermicular sac, continuous with 

 the one from the prostate gland, forming its canal, 

 and toward the apex the other duct. It projects but 

 a short way into the cavity of the great bag, into which 

 it empties its contents. These pass out of the body at 

 the funnel-form opening in the throat. 



The female organs of generation consist of an ova- 

 rium and oviduct. The ovarium is a glandular sac, to 

 which the ova are attached by footstalks. The open- 

 ing by which they issue from the ovarium is wide, 

 and the oviduct (in the Octopus vulgaris and Loligo 

 sagittata,) after continuing a short way simple, di- 

 vides into two branches, each having its external aper- 

 ture near the anus. The oviducts are furnished within 

 with muscular bands, and a mucous lining, and en- 

 circled with a large glandular zone, destined, probably, 

 to secrete the integuments of the eggs. In the Loligo 

 vulgaris, and the Sepia, the oviduct continues single. 

 Besides these organs, the Loligo vulgaris and sagittata, 

 and the Sepia, have two large oval glandular bodies, 

 divided by transverse partitions, with their excre- 

 tory ducts terminating at the anus, whose use is un- 

 known. 



The eggs, whose peculiar form has been already no- 

 ticed, pass out of the funnel, after which they are sup- 

 posed to be impregnated by the male, according to the 

 manner of fishes. 



The inky fluid now remains to be considered, as 

 the most remarkable of the peculiar secretions of this 

 tribe of animals. The organ in which this fluid is se- 

 creted is spongy and glandular. In some species it is 

 contained in a recess of the liver, which has given rise 

 to the opinion that the coloured fluid which it secreted 

 was bile. In other species, however, this gland is de- 

 tached from the liver, and either situated in front or 

 beneath that organ. The excretory canal of this gland 

 opens in the rectum, so that the fluid escapes through 

 the funnel. It mixes readily with water, and imparts 

 to it its own peculiar colour. When dried, it is used 

 as a pigment, and is considered as the basis of China 

 ink. 



The Cephalopoda are all inhabitants of the sea. 

 They are widely distributed, occurring in the arctic as 

 well as the equatorial seas. In the latter, however, 

 they grow to the largest size. It is reported, that 

 in the Indian Seas, boats have been sunk by these 

 animals affixing to them their long arms, and that they 

 are dreaded by divers. 



In the classification of the animals of this class, many 

 difficulties present themselves, in consequence of the 

 imperfect descriptions of their external characters, 

 given by naturalists. In the following general view 

 we shall endeavour to distribute them into natural 

 groups and genera, without attempting an enume- 

 ration of all the species. Such only as are inhabi- 

 tants of the British Seas, shall be particularly enu- 

 merated. 



The Cephalopoda appear to constitute two great di- 

 visions, distinguished by the support which is afforded 

 to the abdominal sac. In the first, which may be 

 termed scpiacea, the sac is strengthened by horny or 

 testaceous processes, unless where the habits of the 

 animal renders such protection unnecessary. The 

 second division, which may be termed Nautilacea, 

 comprehends those animals furnished with a multilo- 

 cular shell. These two divisions, constituted in the 

 Linnsean system the two genera Sepia and Nautilus. 



