210 SYSTEMATIC ZOOLOGY. 



which is coiled in a spiral and is divided by partitions 

 into a series of chambers, only the outer one being occu- 

 pied by the animal (fig. 46). Similarly chambered shells 

 are very abundant among fossils. 



The mouth is armed with a pair of horny jaws shaped 

 much like those of a parrot. These are very efficient in 

 biting food; but any morsels taken into the mouth are 

 subjected to further subdivision by means of the lingual 

 ribbon, which is, as its name implies, a ribbon-like mem- 

 brane, bearing on its surface numbers of minute teeth, 

 which rasp the food into fine shreds. 



The heart is situated in a pericardium and is systemic; 

 that is, it pumps the blood returning from the gills to the 

 various parts of the body. A peculiarity of the circulatory 

 system is that in all, except the pearly nautilus, the vessel 

 carrying blood to the gills develops a special pumping 

 organ, the branchial heart. 



The various ganglia of the nervous system are (except 

 the stellate ganglia) placed close together in the head, and 

 from this centre nerves radiate to all parts of the body, 

 those going to the tentacles being connected with each 

 other by a circular cord. The stellate ganglia, of which 

 there are two, are upon the anterior part of the mantle. 

 The nerves which radiate from them control the motions 

 of the mantle. 



The cephalopods are all marine. They are carnivorous, 

 feeding upon fishes, etc., which they capture with their 

 arms and hold fast by their numerous suckers. The 

 larger forms might be no mean antagonist for man; but 

 the monster described by Victor Hugo is without counter- 

 part in nature. The cephalopods are divided into two 

 orders, according to the number of gills. 



