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As regards any objection to the arguments whicn we 

 have brought against the identity of protoplasm, again, 

 these will lie in the phrase, probably, " difference not of 

 kind, but degree," or in the word "modification." The 

 " phrase" may be now passed, for generic or specific 

 difference must be allowed in protoplasm, if not for the 

 overwhelming reason that an infinitude of various kinds 

 exist in it, each of which is self-productive and uninter- 

 changeable with the rest, then for Mr. Huxley's own 

 reason, that plants assimilate inorganic matter and ani- 

 mals only organic. As for the objection " modification," 

 again, the same consideration of generic difference 

 must prove fatal to it. This were otherwise, indeed, 

 could but the molecularists and Mr. Darwin succeed in 

 destroying generic difference ; but in this, as we have 

 seen, they have failed. And this will be always so : 

 who dogs identity, difference dogs him. It is quite a 

 justifiable endeavor, for example, to point out the iden- 

 tity that obtains between veins and arteries on the one 

 hand, as between these and capillaries on the other ; 

 but all the time the difference is behind us ; and when 

 we turn to. look, we see, for circulation, the valves of the 

 veins and the elastic coats of the arteries as opposed to 

 one another, and, for irrigation, the permeable walls of 

 the capillaries as opposed to both. 



Generic differences exist then, and we cannot allow 

 the word " modification" to efface them in the interest 

 of the identity claimed for protoplasm. Brain-proto- 

 plasm is not bone-protoplasm, nor the protoplasm of 

 the fungus the protoplasm of man. Similarly, it is very 

 questionable how far the word " modification" will war- 

 rant us in regarding with Mr. Huxley the " ducts, fibres, 

 pollen, and ovules" of the nettle as identical with the 



