H!'J ZOOLOGY. 



class is composed. In the octopus, the sepia, and the loligo, 

 there exists only a single pair; but in the nautili there are 

 two pairs. 



600. The heart is situated between the gills, in the me- 

 dian line of the body, and is formed of a single ventricle 

 (Fig. 448, c). The blood reaches it from the branchiae by the 

 branchial veins (vb), whose openings are provided with val- 

 vules, and thus penetrates into the arteries which spring from 

 the organ, and are distributed to the body. This liquid 

 passes afterwards into a venous system, composed partly of 

 vessels properly so called, and partly into cavities without 

 proper walls, hollowed out between the organs ; thus the space 

 comprised around the anterior portion of the digestive appa- 

 ratus performs the office of a venous sinus, and the principal 

 nervous ganglions, as well as various glands, are bathed in 

 the blood. 



Finally, the nourishing fluid which thus returns from the 

 different parts of the body, traversing the visceral cavity, or 

 passing in veins, properly so called, reaches at last a large 

 median trunk, whose branches proceed to the organs of respi- 

 ration, but generally penetrate first into a contractile reser- 

 voir situated at the base of each of these organs. These 

 reservoirs push the blood into the branchial vessels, and con- 

 sequently there are in these animals two pulmonary hearts as 

 well as an arterial; but this arrangement, which exists in all 

 the cephalopoda with two gills, is wanting in the tetra- bran- 

 chial cephalopoda. 



601. The digestive apparatus is very complex. The 

 mouth is surrounded witli a circular lip and with two man- 

 dibles, placed vertically one over the other. They resemble 

 strongly the bill of a parroquet, and are moved by powerful 

 muscles. There are salivary glands, highly developed, several 

 stomachs, and a large liver. The intestine terminates in the 

 branchial cavity at the base of the funnel, by which the water 

 is expired, and communicates with a very singular secreting 

 organ, which in the cephalopodes with two gills produces an 

 abundance of a black liquid, to which the name of ink has 

 been given. The excretory canal of this gland opens near the 

 anus ; and when the animal is in danger, it ejects by the 

 funnel a sufficiency of the dark fluid to colour the surrounding 

 water, and thus escape from the sight of its enemies. It 

 is the ink of one of those cephalopodes, the sepia, which is 

 employed in painting under the name of sepia ; and several 



