24 



ILLUSTRATED NATURAL HISTORY. 



NAUTILI'S WITIIOrr THE SHELL : DIVISION MOLLUSCA. 



ing the animal world, had imposed upon himself, in the beginning, certain fixed rules, from which 

 he would not swerve. 



In this manner we obtain Five Groups or Divisions, each of which leads us a step higher than 

 the others — although it is by no means to be supposed that we have here that gradually ascend- 

 ing chain of beings so much talked of, in which every species, from the lowest to the highest, is 

 supposed to form a link. It is merely in their most highly ore;anized members that the mutual 

 superiority or inferiority of these divisions can be recognized ; and, as a general rule, it may be said, 

 at all event- in respect to the Radiata, Articulata, and Mollusca, that the highest members of each 

 group are considerably more perfectly organized than the lower members of the others. The Pro- 

 tozoa and Veitebrata appear to he exceptions to this rule; for the most highly organized of the 

 former can scarcely be regarded as superior even to the lowest forms of the other divisions, while 

 the lidn -, which constitute the lowest members of the vertebrate division, still appear to be more 

 highly organized than the lowest Mollusca. 



These five divisions are represented in the following classification, though they are presented in a 

 reversed order, it being more according to our habits of observation to begin the study of the animal 

 kingdom with the highest classes, and thence to proceed to those of a lower grade, as they follow 

 in the places assigned to them. 



In regard to this classification, we may remark that, simplicity being a leading object, we have , 

 only presented the divisions of Species, Genera, Order*, Classes, and Divisions, leaving out many 

 subdn isiona of tribes, families, &c, as unnecessary in a table of this nature. In the progress ot 

 the work we shall have occasion to repeat, and in some instances to enlarge upon, the outline 

 given in the preceding pages. 



