Memoirs Nat. Acad. Sciences, Vol. X, No. 3. 



Plate I. 



i i r 



m 



Fig. I. 



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Fig. V. 



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Fig- II. 



Fig. VI. 



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Fig. III. 



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Fig. VII. 



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 Fig. rv. 



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Fig. VIII. 



EXPERIMENT 17. 



