1 62 Mr. Lightfoot’s Account of 
itfelf, as much as is neceffary, when in fearch of food, or in 
the aft of moving from one place to another. 
It may not be amifs here to obferve, that the fepta above- 
mentioned are totally foreign, both in ufe and firudlure , from 
what are called opercula in other fhells : I mean thofe tempo- 
rary covers or ftoppers, made ufe of by many teftaceous ani- 
mals to clofe up the mouths of their fhells, and defend them 
from injury in their quiefcent ftate. 
The opercula, however various in fubftance, are always ob- 
ferved to be fugle, imperforate , moveable at the will of the 
animal, and conftantly placed, as a fecurity, in the mouth , 
never in any other part of the cavity of the fhell ; whereas the 
fepta , in the fubjedb now before us, are repeatedly conftrufted 
in feveral parts of the cavity, are all of them perforated , inti- 
mately connected with the fubftance of the fhell, and confe- 
quently fixed and permanent , as in all the 'Nautili 
And as to the ufe of thefe fepta, though I dare not fay what 
might be the real intention of nature in their formation, yet 
it will be 110 preemption to affirm, that they could not be 
defigned for the fame purpofe as opercula in other fhells ; not 
only becaufe they are placed where they cannot anfwer the 
fame end, but more efpecially on account of their open ftruc- 
ture, which intirely excludes them from the poffibility of 
affording a proper defence to the enclofed animal. 
Should it be laid, that they only ferve to point out the dif- 
ferent periods or fiages of the fhell’s growth, and are nothing 
elfe but the limits or terminations of the animal’s periodical 
increafe, I will not difpute the opinion ; it may perhaps be very 
true ; but fuppofmg it to be fo, is it not equally probable, that 
the tranfverfe fepta in all the Nautili are nothing elfe ? 
But 
