282 THE INHABITANTS OF THE SEA. 



tentacula, with their head downwards and the shell raised above. 

 After stormy weather, as it becomes more calm, they may be 

 seen in great numbers floating upon the surface of the sea with 

 the head protruded, and the tentacula resting upon the water, 

 the shell at the same time being undermost; they remain, 

 however, but a short time sailing in this manner, as they can 

 easily return to their situation at the bottom of the sea, by 

 merely drawing in their tentacles and upsetting the shell. They 

 are caught in baskets by the natives, who eat them roasted as a 

 great delicacy. 



What renders these animals peculiarly interesting is the 

 circumstance that they are the only living representatives of a 

 class which once filled in countless numbers the bosom of the 

 primeval ocean, and whose fossil remains (Orthoceratites, Am- 

 monites) furnish the naturalist with a series of historical 

 documents, attesting the unmeasured age of our planet. What 

 are the ruins, thirty or forty centuries old, that speak of the 

 vanished glories of extinguished empires to these wonderful 

 medals of creation that lead our thoughts through the dim 

 vista of unnumbered centuries to the fathomless abyss of the 

 past. 



In point of development of organisation the Gasteropods or 

 snails rank immediately after the Cephalopods. They also have 

 a head plainly distinguishable from the rest of the body, and to , 

 which two brilliant black eyes give an animated expression. 

 But their nervous system is far less developed, and while the 

 lively cephalopod is able to swim about, and rapidly to seize a 

 distant prey, almost all the gasteropods creep slowly along 

 upon a fiat disk or foot situated below the digestive organs, a 

 formation to which they owe their name of gasteropods or 

 stomach-footers. 



The marine snails are divided into several groups according 

 to the different position and arrangement of their gills. In 

 some species these organs form naked or free-swimming tufts 

 on the back (Nudibranchiata) but generally they are variously 

 disposed either in special cavities or under the folds of the 

 mantle. Thus in the Inferobranchiata they are arranged 



