THE NAUTILUS. 311 



Argonaut drives itself backwards at a rapid rate, by 

 alternate imbibition and expulsion of water through its 

 siphon. The Pearly or Chambered Nautilus is the shell 

 of another animal of this class, considerably different in 

 organization from the Cuttle-fish or the Argonaut, and 

 obviously of a lower type of structure. It essentially 

 differs from either in having four, instead of two, sets of 

 gills, and has therefore been placed by Professor Owen 

 in a distinct order, of which it forms almost the only 

 living representative. Very different, however, was the 

 condition of this order in the waters of the early world, 

 where species of Nautilus and of allied forms existed in 

 great profusion. Upwards of sixty fossil species of 

 Nautilus are found in British strata, with many hun- 

 dred kinds of Ammonites, Orthoceratites, &c., genera 

 which are no longer known to exist in a living state. 

 And it is exceedingly remarkable that our modern Nau- 

 tilus belongs to a generic type which has existed from 

 the earliest times, from which remains of animals of this 

 class have been preserved ; while many extensive genera 

 of similar animals of later creation have become totally 

 extinct. Thus, of the true Ammonites, or Snake-stones, 

 fossils resembling the horns of Jupiter Ammon, and 

 which were inhabited by animals resembling the animal 

 of the Nautilus, though many hundreds flourished in 

 times long posterior to the creation of Nautili, and none 

 were in existence so early as the first true Nautilus, not 

 one has come down living to the modern sea, and the 

 last members of the race were entombed in the chalk 

 deposits. The successive changes which have passed 

 over the animal and vegetable worlds in revolving ages 



