We have seen that one of the deep-sea Crustaceans has phosphorescent bands upon its feet; and in the _Syllidæ_, a family which contains some remarkable worms, we find that the luminosity is confined to the under surface of the feet. In _Chætopterus_[33] a bright flashing light is emitted from the posterior feet, while a far more brilliant one glows at a point on the dorsum between the lateral wings of the tenth segment. The mucus of the animals appears to be the seat of the luminosity, and not only encircles the worm with an aureola of phosphorescence, but pervades the surrounding water with a rich bluish purple light, so vivid and brilliant that the medium in which the light-giver lives seems to have ignited, and to be slowly consuming its dependents. [Illustration: PLATE VII. BURROW OF PHOLAS. SEA PEN. (_Pennatula._)] It has been noticed, according to W. C. McIntosh, that an odor accompanies this display, resembling somewhat that produced by phosphorus in combustion. We have noticed that many worms have a peculiar odor when handled, though not quite of this character. The most brilliant of all these light-givers is _Polycirrus_, which emits over its entire surface a vivid pale-bluish light, marking it as one of the most beautiful of its kind; while _Sagitta_ and many more add to the wonders in this generally considered uninteresting group of animals.[34] CHAPTER VI. LAMP SHELLS. In all the forms previously mentioned, the phosphorescence is conspicuous; but in the little bivalve Pholas it is almost hidden. The shells of the family _Pholadidæ_ are noted for their boring habits; penetrating into the hardest stone, as granite and gneiss, literally entombing themselves, as shown in Plate VII., Fig. 1, which represents a section of a block of granite into which the little animals have penetrated. How they can perform such a work, is something of a mystery; but the foot, which is provided with a hard dermal protection, is probably the instrument used by the miner. The most remarkable evidence of their work, according to Figuier,--though it is fair to say he has been disputed,--is seen in the Temple of Serapis on the Pozzuolan coast, where the pillars are perforated with holes, which this author claims were made by the Pholas,[35] when by a sinking of the crust the pillars were under water; the columns, by a reverse motion, having now re-appeared from the sea, bearing the evidences of their submersion.