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present my object is to compare, not organs with 

 functions, but first organs with organs, in order 

 to trace the analogies, as well between the dif- 

 ferent organs of each animal, as between the 

 corresponding organs of different animals ; and 

 subsequently functions with functions, in order 

 to trace their mutual dependence on each other. 

 I have elsewhere remarked that it is by a 

 union of more or fewer of the tissues, composing 

 an organized being, that its several organs are 

 formed ; and the power by which this union of 

 the tissues, or organization, is effected, has been 

 long known by such various names as Vis Plas- 

 tica, Nisus Formativus, &c. So far, however, 

 giving a name to this power is equivalent only 

 to admitting its existence, and tells us nothing 

 whatever, either of its nature, or the laws by 

 which it operates. It is, in the language of Ham- 

 let, merely " words, words, words !" but some 

 modern Physiologists have endeavoured to push 

 the matter beyond mere words, and to discover 

 and demonstrate some definite laws, by which 

 organic elements, or tissues, are combined to 

 form organs many of which may be essentially 

 the same in their organic structure, however 

 various their form and functions in the same 

 way as the particles of crystals are combined to 

 form salts, several of which have one common 

 primary character, however different their aspect 

 and properties. This idea seems to have originat- 

 ed in so far at least as it is a modern one in 

 Germany, and has been prosecuted principally 



