CEPHALOPODA. 



355 



iusca ; but in the Argonaut and in all the Decapoda, it manifests its 

 distinct function by its separate position. The liver issurrounded by 

 a smooth capsule, and is not subdivided externally into lobules, as in 

 the Nautilus and lower MoUusca. The biliary ducts in the Octopoda 

 are simple canals, which unite and terminate by a common orifice, 

 in the pancreatic sac. In the Decapoda they receive the ducts of 

 numerous clusters of caecal appendages beyond the smooth part of 

 the liver. 



The ink-bag consists of tough white fibrous texture, the outer sur- 

 face of which is coated by a thin silvery or nacreous layer : its inner 

 surface presents a fine spongy glandular texture. It presents a trilobate 

 form in the Sepiola, and an oblong pyriform shape in the Sepia and 

 Loligo. It is a very active organ, and its inky secretion can be re- 

 produced with great activity. The tint of the secretion varies in dif- 

 ferent species, as is exemplified by the Italian pigment called ' sepia,' 

 and the Chinese one, called ' Indian ink.' It is of a very indestructible 

 nature, as is exemplified by its frequent preservation in a fossil state 

 in both the extinct Calamaries and the Belemnites. It is affirmed 

 by some chemists to contain a peculiar animal principle, which Vizio 

 has termed ' melanine.' 



Many of the Cephalopods possess the power of emitting a luminous 

 secretion. All of them are nocturnal and social animals, and are 

 readily attracted by bright metallic substances. 



Prior to the dissection of the Pearly Nautilus, the Cephalopods 

 ■were regarded as having three distinct hearts ; but two of these, which 

 are appropriated to the branchial circulation, are peculiar to the higher 



order, and are perhaps 

 the main-spring of their 

 superior muscular ener- 

 gies. 



In the Dibranchiata 

 the venous blood returns 

 from each arm along 

 its lateral and posterior 

 parts by two veins, which 

 severally unite at the 

 base of the arm with the 

 opposite vein of the ad- 

 joining arm, the whole 

 being ultimately convey- 

 ed to an irregular circular 

 sinus, which is continued 

 Sepia officinalis. between the head and 



A A 2 



