13 



maining fibres of the body as centres, the fibre itself, when by 

 this process hermetically sealed up, would remain there to this 

 day in much the same condition as it then was, usually more 

 or less charged with sulphuret of iron ; and that, where not so 

 hermetically sealed, it would, on its subsequent decay, either 

 leave the incrusting calcedony in the condition of a series of hol- 

 low tubes, or such hollow tubes would, still subsequently, be again 

 filled up by a continuation of the process of siliceous crystalliza- 

 tion. I have many specimens of the Ventriculidse in each of these 

 conditions. It will further be obvious, that where, as occasion- 

 ally might happen, but comparatively rarely, because dead fibre 

 would have less attraction for the siliceous fluid than soft animal 

 matter, the fibrous skeleton of an animal of which the soft parts 

 had already decayed away was enveloped in the siliceous fluid, no 

 hollow would ever be formed, but that fibrous skeleton would be 

 preserved hermetically sealed. I have instances of this latter 

 mode of preservation also. 



The flint specimens are, in the vast majority of cases, found 

 with flint on both sides ; a fact resulting, there can be little doubt, 

 from the operation of some cause connected with electricity, 

 which, though there is in no part any communication between 

 the two surfaces, determined an attraction and affinity between 

 equivalent masses of siliceous fluid on the two opposite sides, just 

 as we see the needle follow the magnet though a solid plate in- 

 tervene. Cases are however not very uncommon in which the 

 flint exists in a mass only on one side, there being on the other 

 merely narrow filamentous threads of flint. When the mass is 

 thus found on one side only, that side is, in almost all cases, 

 the inside. Now the Ventriculites being funnel-shaped, there 

 would necessarily be a much greater attraction for the siliceous 

 fluid on the inner side of the body than on the outer side, in pre- 

 cisely the proportionate difference that there is between a single 

 exposed plane surface and a surface closed in on all sides by op- 

 posite surfaces. If a mass of siliceous fluid were not great in a 

 particular spot, the greater part of it would thus be drawn to the 

 inside, the electric attraction before hinted at operating however 

 generally to attract a small portion to the outer corresponding 

 surface, where it would spread in what now appear as filamentous 

 threads between the foldings of the outer surface of the animal, 

 in which spots the greatest attraction on the outside would of 

 course be, in consequence of the opposite surfaces there present*. 

 Occasionally a similar appearance is found both on the external 

 and internal surface ; but that is usually towards the margin of 

 a flint which is otherwise encased on both sides, as in the speci- 

 men fig. 2- of my paper of January, and betokens an exhaustion 



* See and cf. p. 9 and note to p. 301 of the two articles before referred to. 

 The threads of flint are there found though the body was not encased. 



