APPENDIX. 177 



of appreciation of the fact that Darwin intended this 

 theory merely as a temporary mental picture, and 

 nothing more. 



But Weismann puts forward his views in most 

 sober earnest, elaborates the details of his theory, and 

 remodifies his conceptions so that his story may fit in 

 with the fresh discoveries in embryology and com- 

 parative anatomy as these are made. Our criticism 

 is simply this, that the hypothesis, being nothing more 

 than a personal conception of the author's, is not to be 

 tested by experiment, and that the author could 

 always escape from the clutch of refutation. We are 

 left, moreover, in the same difficulty with which we 

 started, for by giving his living units the functions of 

 growth and reproduction, which must involve heredity 

 itself, Weismann shunts back the question from 

 animal and plant, which we can see and handle, to 

 particles quite beyond our ken. We may also point 

 out that there is no reason to assume that living 

 matter is made up of little parts, or persons, molecules 

 or groups of molecules ; experiment, in fact, strongly 

 contradicts this assumption. Let us see how human- 

 ity first obtained the idea that matter is made up oi 

 little bits, how we obtained the idea of molecule or 

 atom. The idea is an ancient one, and it is easy to see 

 how it occurred to thinkers even in primitive times. 

 Most solids, such as chalk, sand, and rock, and fluids 

 too and gases, are, when broken or divided, of ob- 

 viously similar parts. If we break a piece of writing 

 chalk across, each fragment of it is chalk that is, it 

 appears to us to be white and hard, it will write upon 



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