MOLLCSCS. 



363 



space will at present allow us to allude, tliat of the jwjier sailor, Argonmita. In this 

 genus the shell is without connection with the body, but is secreted by two of the 

 arms, which are greatly expanded for 

 the purpose, and serves as a nest for the 

 eggs. 



The mouth of tlie cephalopods is 

 armed with a pair of beaks like those of 

 a parrot, with sharp cutting edges. In 

 the Nautilus these beaks are calcified, 

 but in all other living forms they are 

 horny. Between the jaws is the tongue, 

 and below them is a lingual ribbon, to 

 all intents and purposes like that of the 



, , , -,,/,, T-. , • -I , Fig. 474. — .•(/■(70Hat((a with shell broken to show tile eggs. 



ceplialophorous MoUusca. Behind the 



lingual ribbon begins the usually narrow cesophagiis, into which one or two pairs of 

 salivary glands pour their secretions. The (Esophagus empties into the stomach, 

 which is of moderate size, but strong and muscular, and provided with a blind a]>pen- 

 dage (cajcuni), which frequently is larger than the stomach itself. From the stomach 

 the intestine goes forward in a course nearly par.allel to that followed by the ccsopha- 

 gus, and terminates in a median vent on the lower surface of the body just within the 

 siphon. The liver is large, and opens into the cascum. In the dibranchiate forms 

 there is an ink-bag, borne near the intestine, and pouring its inky secretions into the 

 rectum, or into the mantle cavity through an opening near the anus. The ink is brown- 

 ish or black, and is used to create a cloud in the water when the animal wishes to 

 escape from some danger. The ink is not readily decomj^osed ; on the contraiy, it is 

 occasionally found fossil in the rocks along with the remains of the animal which pro- 

 duced it. So well has it been preserved that in one 

 celebrated instance a naturalist drew the portrait of a 

 fossil squid with the sejiia derived from its fossil, but 

 not fossilized, ink-bag. 



The circulatory system is well developed in all' the 

 cephaloi^ods, especially in the higher groups. The de- 

 tails would prove dry reading, and so we will merely 

 mention a few facts. There is only one ventricle, but 

 the auricles m.ay vary from two to four, in accordance 

 with the number of gills. On each vein going to the 

 gills is a pulsating vesicle, the branchial heart. It is 

 in the problematical appendages to these that the 

 curious worms, Dicyemida, referred to on a preceding 

 page, have been found. In some true cajiillaries are 

 ]f^' developed, while in others the .arteries terminate in the 

 lacunaj of the body. We have just referred to the ex- 

 istence of one or two pairs of gills. This character is 



FiG.475.— Nervous system of female A'ari- • ._ n -.i ^i i • i • ^i ■ n 



tihis: b, branchial nerve; c, cerebral associated With Others, and IS used HI the naming and 



ganglia: (>, olfactory organ; or, oviduct, t f« ... r ^i 4. • T-i*i i ■ i i 



P, pedal ganglion; r, visceral ganglion; definition 01 the two ]u-miary groups, Dibraucliiata and 

 s, optic nerve. Tctrabranchiata. Correllated with this variation in the 



number of gills and hearts is one in the kidneys, wliich are also two or four in number. 



It is in these points only that any metamerism of the cephalopods is noticeable. 



