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the shells of Molluscs ; Mr. Eainey had long ago pointed out that mineral sub- 

 stances, such as carbonate of lime, when crystallising in a colloid fluid, were very 

 prone to form spheres and dumb-bell crystals. According to Mr. Green's descrip- 

 tion the shield of a diatom seemed to consist of an aggregation of similar 

 pellets of silex, the convex markings, or beads, being the surfaces of crystal- 

 line pellets, and the spheres being modified into hexagonal prisms by mutual 

 contact with a segment of a sphere at their free surface. It would be seen at 

 once that this theory would not account for the crater-like pits on the surface ; 

 but the appearance of these depressions brought to his (Mr. Lowne's) mind 

 the almost irresistible idea that they resnlted from disintegration and solution 

 of the surface of some of the flinty pellets; they are undoubted erosions with 

 ragged edges. Of course he only suggested this view as a pure hypothesis, but 

 it did seem to him probable that if absorption or solution of the flint laid down 

 were going on simultaneously with deposition at certain points, it would account 

 for the appearance. 



Mr. T. C. White said that however much he might admire it he felt he must 

 demur to some portions of the beautiful theory which Mr, Lowne had built up. 

 One fatal objection to the idea of the diatomacese being formed by crystallization, 

 as in Mr. Rainey's experiments, appeared to be the perfect regularity of their 

 surfaces ; such crystals formed in merely a colloid substance would be irregular 

 in size, instead of being so perfectly regular, as were the diatom markings. 



Mr Lowne, in reply, said that with regard to Mr. White's objection, he believed 

 it to be merely founded on a misapprehension of the conditions under which 

 these crystals would be formed. He believed that under such a medium as he 

 had supposed, the silica would be deposited with regularity, because the laws 

 under which its deposition took place were the same all over the shield, and 

 there appeared to be no reason why one pellet should be larger than another. 

 Nobody would, of course, attempt to maintain that the silica was alive. What 

 they had there was a simple mechanical support or skeleton, the structure of 

 which still appeared to him to bear a strong analogy to the deposition of carbo- 

 nate of lime from a colloid solution, such as is seen in the shells of the mollusca. 

 He believed the subject might be easily worked out by observing the development 

 of the shields of some of the larger diatomacese. 



Mr. Ingpen hoped that the ingenious speculations which had been advanced 

 would not lead members away from the subject of the paper, which was a really 

 practical one. He should himself like to ask for some more information as to the 

 modus operandi, and would be glad to hear whether the light was thrown upon 

 the object parallel,— whether it comes through slits, or what was the process ? 

 He thought they ought not to let this paper sleep without some further investi- 

 gation. 



Mr. Breese thought that the view taken by Mr. Lowne was open to some 

 negative evidence, and suggested a mode of examining diatoms, which, he 

 believed, would be found very useful. His plan was to obtain an ordinary slide 

 3 X lin., and to wrap round it a quantity of fibrous glass, such as that of which 

 the glass peacocks' tails were made, and then, having floated upon it some of the 

 diatoms, cut the glass fibres, and they would have the diatoms propped up upon 

 the fibres in such a manner as to enable them to be examined with great advan- 

 tage; a very brief examination would show that it was bad to view them 

 through covering glass, or any other medium. The result of his observations 

 was that he could most fully bear out the remarks of Mr. Green. Viewedinthe 

 manner he had described, they conveyed to his mind the idea of the shape of 



