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CHAPTER V. 



QN CLASSES, OR THOSE NATURAL GROUPS INTO 

 WHICH THE ANIMAL KINGDOM MAY BE RE- 

 SOLVED ON ITS SECOND RAMIFICATION. 



ANIMALS appear to have been created on two distinct 

 plans; or, to make use of an idea frequently adopted in the 

 course of this work, nature seems in the animal kingdom 

 to have set out from inorganic matter by two different 

 routes, which meet together and complete the circle among 

 the Annelides, or Crustacea. This difference of construc- 

 tion may be thus represented : although properly speak- 

 ing the rule applies only to the greatest part of the An* 

 nulosa, and not to the Crustacea or Arachnida. 



C ACRITA, 

 Animals in which no circulation j tjatuata 



of blood is visible, ^Annulosa. 



Animals in which the circulation { VERTEBRATA, 

 of blood is perfectly distinct, ( MoLLUSCA. 



In this last plan there is constantly a pulmonary or 

 branchial respiration aimed at, with a perfect system of 

 circulation for the nutritive fluid ; in the other, not only is 

 the existence of a circulation a question to which no small 

 degree of doubt may be attached, but the system of respi- 

 ration is of a nature quite different and apparently much less 



