SHELLS. 219 



The neryous system consists of a central part or 

 brain, situated above the intestinal canal ; of ganglia 

 for the different organs of sense, as well as for the 

 locomotive apparatus; of a few visceral ganglia, 

 together with conducting filaments or nerves. 



To the first class of Mollusca belongs the Cepha- 

 lopoda (or head-footed). The fleshy, flexible feet 

 are instruments of locomotion, the animal being 

 enabled to crawl awkwardly upon this circle of feet 

 head downwards. But their chief use to the animal 

 is as organs for seizing and holding prey, and for 

 this purpose they are eminently quahfied. Each 

 arm is furnished with a double row of sucking disks, 

 each of which, on being applied to any surface, 

 adheres to it at the will of the animal with immense 

 force, so that it is easier to tear away the substance 

 of the limb while the creature maintains its hold, 

 than to release it from its attachment ; and even 

 after death the suckers continue to retain a consider- 

 able power of adhesion. 



The skin of these animals, particularly of the 

 Octopus, changes colour, in patches and in spots, 

 with a rapidity greatly superior to that of the 

 chameleon. 



These animals are voracious and savage ; and as 

 they are agile, and are furnished with numerous 



