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Ibalt^'lbours at tbe flDicroscopc witb tbe 

 late flDr. Znttcn meet 



Plates XXII., XXIII., XXIV. 



Arborescent Crystallised Silver (Plate XXII., Fig. i). — I'hisis 

 truly a lovely slide ; when viewed as an opaque object with the 

 light well directed, it is strikingly beautiful, and will tem[)t many 

 of us to try, by repeating the mounter's experiment, to get its 

 counterpart for our own collection. I have never seen any so 

 perfect of its kind as this is. Its wonderful resemblance in minia- 

 ture to vegetable growth is well seen by comparing it with the 

 algae, Angiunaria dilatata, happily present in the same box as if 

 for the purpose of comparison. The juxtaposition of the pair 

 suggests thoughts like these : — In each case we have a substance 

 in solution, to begin with —the one a mineral salt, the other vege- 

 table protoplasm. The essential correspondence in the angle 

 assumed by the branches with regard to the main stems indicates 

 that the deposits i?iust have been laid in obedience to the same 

 fundamental view, magnetic currents being doubtless the imme- 

 diate agents, copper having a stronger affinity for some nitric acid 

 wedded to silver, robs the latter and sets free the Dian metal. In 

 the second case, by the play of affinities less easy to comprehend 

 in their entirety, a corresponding force separates what we see here, 

 and lays it down as vegetable growth, on a well-recognised plan, 

 which bears its appropriate name : the " formed material," in one, 

 Pure Silver ; in the other, an "alga." The idea might be extended 

 so as to embrace the Animal Kingdom, in which some of the 

 Sertularian Zoophytes probably show the nearest approach to 

 deposition on the like plan. 



Spines of Spatangus (PI. XXII., Figs. 2, 3, 4, 5, 6).^ — " Spa- 

 tangus " is one of the " Heart Urchins." By careful consideration 

 of this specimen, and comparing it with an entire example, we 

 learn that the piece of shell with its attached spines, here shown, 

 has been taken from the right side near the position of the vent. 

 Study of the figures on the Plate, with their explanation, will, I 



