side of which is attached by a short footstalk the beautiful pall-like leaflet, and on the under side a similar smaller one, the tip of the foot projecting between them. This point is perforated to give emission to the pencil of bristle-spears, which are arranged like a fan, and are, at the will of the animal, projected to a considerable length from the foot, or withdrawn completely into its interior, as into a sheath. Each individual bristle is composed of a very slender, long, straight shaft, terminating in a knob somewhat resembling the end of a limb-bone. This is slit in one direction to receive the terminal lance-head, which is fitted into it exactly as a knife-blade is fixed into its handle. It is in fact a knife-blade having a thickened back, and a very thin edge, which is notched with teeth of the most delicate subtilty. The blade is slightly curved, and drawn out to a long acute point; and the whole space is formed out of a substance that rivals the purest glass.
The full use of these most exquisitely contrived and finished organs is, I think, yet to be discovered. They are doubtless instruments of locomotion, being evidently used to push the animal along, as a ferry-man propels a boat with his pole; and the saw-like teeth may serve to catch the roughnesses of the surfaces along which it is moving. It is possible also that they may be weapons of defence; for, being thrust out at every laternal undulation of the segments, they present formidable chevaux de frise to any small enemy who may entertain malice prepense againt the Annelid. Still the situation of these arms is hardly such as we should expect, if this were their primary
