THE SQUIDS, CUTTLEFISHES AND NAUTILI 3295 



quently termed naked mollusks. Nearly all decapods, that is, those species which 

 are provided with ten so-called arms have a straight calcareous or horny internal 

 shell, which is a strengthening support to the back. Spirula, however, although a 

 decapod, is an exception, and possesses a segmented shell, coiled up like a ram's 

 horn, and concealed within the hinder part of the animal's body. The external 

 shell wherein the female argonaut dwells is not the equivalent of the shell of the 

 nautilus, or of the gastropods. It is not attached to the animal by any special 

 muscle, but held to the body by two of the arms especially developed for this pur- 

 pose. It is in fact, merely a receptacle for the ova, but at the same time affords 

 protection to the argonaut herself. All the rest of the octopods are without shells 

 of any description. 



The body of a cephalopod consists of a muscular sac, in the cavity of which 

 the viscera are placed. In front of the body projects the head, which, in one of 

 the two main sections into which the class has been divided namely, the 

 Dibranchiata, or those provided with only one pair of gills is crowned with eight 

 or ten fleshy muscular arms, in the midst of which the mouth is situated. This is 

 armed with two strong jaws, in shape very similar 

 to the beak of a parrot. They are curved, 

 pointed, and of a horny substance in the two- 

 gilled cephalopods, and somewhat calcareous in 

 the four-gilled group. Within the mouth is the 

 rasping tongue, covered with the sharp siliceous 

 hook-like cusps or teeth, arranged in regular UPPER (a) AND W>WER (*) PORTIONS 



,,.,,, mi OF THE BEAK OF A CUTTLEFISH 



transverse series, one behind the other. The (Sepia) 

 eyes, two in number, are placed on each side of 



the head, and are of enormous size in some of the decapods. On the ventral side 

 the muscular sac is disconnected with the head, leaving a more or less wide open- 

 ing admitting the water to the gills. The water is then expelled through the so- 

 called funnel with more or less force, according to the requirements of the animal. 

 If it be at rest, the expulsion of water is carried on very quietly, but, on the con- 

 trary, with much greater force, if the animal is in motion. Besides water, other 

 secretions from the body are extruded through the funnel, and especially a dark 

 fluid secreted in a special ink pouch. When disturbed or irritated, this ink is dis- 

 charged by all cephalopods, excepting the nautilus, and is supposed to be a means 

 of defense. Mixing with and clouding the surrounding water, we can well suppose 

 that the attack of a pursuing fish might be checked, and the squid or cuttle effect 

 its escape in the darkened fluid. The arms, or feet, of the octopods and decapods 

 are more or less elongate and capable of movement in any direction, and are fur- 

 nished on one side with numerous suckers, by means of which the animal holds on 

 to anything that it may seize with such tenacity that the suckers themselves are 

 liable to be torn away rather than loose their hold. They are often furnished at 

 the edge with a toothed horny or calcareous ring, and connected with the arms by 

 slender stalks. Cephalopods employ their arms in walking and climbing, and, 

 owing to their position, have to progress head downward when creeping on the sea 

 bottom. They are connected at the base by a skin, in some species extending some 



