ORGANIC AND INORGANIC MATTER COMPARED. 65 



petually taking place. Change, in short, is one 

 of the grand characters of vital organization ; 

 while permanence is that of a crystal, till its 

 form is destroyed by an extrinsic, not intrinsic, 

 agent. 



Organic beings have all, more or less palpa- 

 bly developed, a central form, to which are 

 attached members, diversely modified, but 

 essential to their well-being. The exceptions 

 to this rule, as in the case of the sponge — if wo 

 can include it within the animal kingdom — and 

 of certain gelatinous corpuscles, regarded as 

 coming within the domain of the vegetable 

 world, need not here be taken into the account. 

 On the whole it may be said, that animals as 

 well as plants have " a more or less rounded 

 or cylindrical form, branched or membered, 

 bounded by curved lines, and by convex or 

 concave surfaces, very distinct from the crystal- 

 line, the only regular form of inorganic matter." 

 In all animals, the form is definite even when 

 precise symmetry is wanting ; in most, how- 

 ever, form is symmetrical as well as definite. 

 Our distinction may be thus illustrated — bivalve 

 mollusks, as the oyster, are definite in form, 

 but*not symmetrical ; the nervous ganglia, the 

 limbs, or appendages, the aerating organs, etc., 

 do not balance each other in and around a 

 central mass. But in the classes of quadrupeds, 

 birds, reptiles, and insects, as well as Crustacea, 

 (crabs, lobsters, etc.,) the nervous system, whe- 

 ther a true brain be present or wanting, is 

 symmetrical, the limbs are symmetrical ; for 

 c 



