6 MOLLUSCA. 



side, resembling a highly complicated fern leaf ; the great vena cava, 

 having arrived between them, divides into two branches, which 

 pour their contents into two fleshy ventricles, each of which is 

 placed at the base of the branchiae on its own side, and propels the 

 blood into it. 



The two branchial veins communicate with a third ventricle, 

 situated near the bottom of the sac, which, by means of various 

 arteries, distributes the blood to every part of the body. 



Respiration is effected by the water which flows into the sac and 

 issues through the funnel. It appears that it can even penetrate into 

 two cavities of the peritoneum, traversed by the vena cava in their 

 passage to the branchiae, and act upon the venous blood by means of 

 a glandular apparatus attached to those veins. 



Between the bases of the feet we find the mouth armed with two 

 stout horny jaws, resembling the beak of a parrot. 



Between the two jaws is a tongue bristling with horny points ; the 

 oesophagus swells into a crop, and then communicates with a gizzard 

 as fleshy as that of a bird, to which succeeds a third membranous and 

 spiral stomach, which receives the bile from the two ducts of the very 

 large liver. The intestine is simple and short. The rectum termi- 

 nates in the funnel. 



These animals are remarkable for a peculiar and intensely black 

 excretion, with which they darken the surrounding water when they 

 wish to conceal themselves. It is produced by a gland, and retained 

 in a sac, variously situated, according to the species. 



Their brain, which is contained in a cartilaginous cavity of the 

 head, gives off a cord on each side which produces a large ganglion 

 in each orbit, whence are derived innumerable optic filaments ; the 

 eye consists of several membranes, and is covered by the skin which 

 becomes diaphanous in that particular spot, sometimes forming folds 

 which supply the want of eyelids. The ear is merely a slight cavity, 

 on each side near the brain, without semicircular canals or an exter- 

 nal meatus, where a membranous sac is suspended which contains a 

 little stone. 



The skin of these animals, of the Octopi particularly, changes 

 colour in places, by spots, with a rapidity which greatly surpasses 

 that of the cameleon.* 



The sexes are separated. The ovary of the female is in the bottom 

 of the sac : two oviducts take up the ova and pass them out through 



* See Carus, Nov. Act. Nat. Cur., XII., part I, p. 320, and Sangiovanni, Ann. 

 dts Sc. Nat. XVI, p. 308. 



