with Observations on their Structure and Colour. 41 
animal, as I imagine, that, by fine injection, I should have dis- 
covered the vascularity of this gluten, and, probably, inflamma- 
tion in the contiguous parts. No one doubts the existence of 
such an animal-nidus in bones and shells, who is acquainted 
with the process commonly used for exhibiting it, by dissolving 
their earth in dilute muriatic acid. Shells, in this process, lose 
their colours, and I find that pearls equally lose theirs, having 
dissolved blue and brown as well as common pearls, which gave 
me equally balls, almost without colour, or of a faint yellowish- 
brown, consisting of concentric membranes, and so light, that 
from same air-bubbles included, though not visible to the naked 
eye, they swam in the acid. 
These experiments I made many years ago, and, more late- 
ly, I commenced others of a similar nature, but better 
planned, introducing, in place of pointed wires, round beads 
of different materials, through holes in the shell. These beads 
were of glass, steel, &c., and, from their form, I supposed would 
produce less irritation, and afford a fairer surface for the adven- 
titious earthy matter. What I here attempted by art, is not 
unfrequently produced by nature herself. 1 have two scallop- 
shells (the flat-shell), the inner surface of which is very thick, 
and set with extremely minute points of the substance of the 
shell, which, it appears, the animal had, in this instance, also 
produced in its own defence, in order to guard itself against the 
invasion of a species of boring molluscous animal, which had made 
its way through the outer layers of the shell, and was proceeding 
inwards, so as to oblige the animal to secure in many points its 
inner wall against the invader. These shells seem to point out 
two facts: 1st, That the animal, being under the necessity of 
depositing its shelly matter in certain weak points, does not seem 
to have confined itself to these points only, but, having once be- 
gun the process, to have deposited its new matter in many other 
places. If I am deceived in this conjecture, it is probably on 
account of the extreme minuteness of many of these points, 
where the borer had attacked the fish, and which appear to our 
eyes as depositions without a cause, and made at random. 2dly, 
That pearls will differ in colour, according as the animal is em- 
ployed at the time of their formation in producing the coloured 
or colourless part of its shell. Thus, we have orange-coloured 
