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LETTER XIII. 



ON THEIR CIRCULATING SYSTEM. ' '^ 



ARISTOTLE divides animals into those which have blood, 

 and those which have none ; and these primary classes were 

 appropriately named the sanguineous and exsanguineous. 



Fig. 36. 



a, Veil ; 6, tentacnla ; c, neck ; rf, organs of generation ; e, anus and another excre- 

 tory orifice ; f, greater branchiae ; g, lesser branchiae ; A, margins of foot. 



Among the latter, he places the mollusca, as all naturalists 

 did for a long time afterwards, and as all, except naturalists, 



