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 which in some is more than thirty times the length of the cell, into which it returns. I am apt to think, that this gut or ductus, as well as the body of the creature, is capable of being extended very considerably, to serve all the uses of forming the Belemnite, without leaving the siphunculus; and that the gut serves for the same purposes with the tendons of the oyster; the latter to open and shut the shell; the former to allow the animal to go out and in at pleasure. And as the oister feeds altogether in the shell, by opening the verge, the Belemnite (whose residence is in the great deep, which is seldom disturbed) very likely goes out in quest of food, but travels only upon the guard or rampart, leaving a trail behind, as all land snails do; which hardening into a testaceous substance, increases the dimensions of the outer walls, both in length and thickness, from the cell or chamber, to the bottom or point of the whole Belemnite. The animal in its progress and return clasps the whole guard, as a snail does a small branch of a tree in the gardens; and where the two sides meet, there the sulcus is formed, as is evident from the laminæ in Fig. 9.

The Belemnites, like all other testaceous bodies, have the vermicular tribe attached to them, and are perforated by the pholades. Other marine bodies also affix themselves to the Belemnites, oisters in particular: but this never happens whilst the animal inhabits the shell, because the new additional laminæ would so cover the affixed body, and also the cells of the pholades and vermiculi, that they could have no communication with the water, and must consequently

LIV.