[ 4 ] 
The texture of the fhell is very- thin and brittle; 
and therefore it is wonderful to 'fee the holes they lie 
in fo fmooth and uniform, as if bored with a hard 
fharp inftrument. The bafe end is always inward, 
and the hole which opens from them outwards very 
fmall ; and this is the cafe of every kind which are 
thus lodged whether in wood or done j fo that one 
muft conclude that they are depofited there in a very 
minute date, and not in a date of maturity ; for 
then they muft bore their way inwards, and the hole 
would be as wide outwards as inwards, and confe- 
quently be of equal diameter. But how thefe ani- 
mals maintain and increafe the cavity, as they grow 
larger, is a queftion which it will be very difficult to 
refolve, and has puzzled feveral ingenious naturalifts 
in the enquiry. 
It is faid they have a power of turning themfelvcs 
about wdth a fwift motion, and fo make themfelves 
gradual room ; but this will be hard to conceive, if 
we confider that a fifh clofely ffiut up within its 
valves, and comprefled on all fides, can have no power 
of motion. We cannot imagine any animal can move 
itlclf, when thus confined, without fome fulcrum 
or point of effort, from which to begin fuch motion ; 
and if they had fuch tentacula as were capable of 
feizing upon the wood, in order to exert themfelves, 
there can be no room for it, for it is in clofe contadt 
with themfelves in every point. That this is the 
cafe, is very clear, from confidering the ftate of toads, 
frogs, and other animals, inclofed in blocks of marble, 
trunks of trees, &c. which have no communication 
with the atmofphere at all. Thefe are foft animals, 
and their fhape not at all fit for turning about and 
I boring 
