Two years since, my friend Mr. Charles Stewart, then residing at Plymouth, told me of certain Annelids which were in the habit of perforating limestone rock in that neighbourhood, and which he had found, when removed from their excavations and placed on blue litmus-paper, to give a strongly acid reaction. Soon after this, I received, by his kindness, specimens of this Annelid, which proved to be a Sabella
, described by De Quatrefages as Sabella saxicava
, and abounding on certain limestone coasts. The species is a small one, forming a dirty-looking leathery tube, about one inch and a half in length. Of this, one inch is buried in a perfectly cylindrical and straight excavation in the limestone, to the walls of which gallery the tube closely fits; the other half inch of tube projects freely from the surface of the rock (PI, XI. fig, 4).
Having had my attention called to the subject, I remembered certain perforated stones and pebbles abundant on the south coast of the Isle of Wight, which seemed to me to be very possibly the work of an Annelid; and when there, a year since, I searched carefully for specimens. Below the Lower Greensand cliffs near Luccomb Chine there are but few large calcareous boulders on the shore, though there are many of indurated sandstones, of varying hardness and colour. Not a fragment of the sandstones, though some were very soft, exhibited a single worm-perforation; but wherever a boulder consisting largely of carbonate of lime lay between tide-marks, it was more or less excavated by minute passages; and these in many cases were so numerous that it was obvious that the author of these "riddlings" must play an important part in the destruction
and solution of such masses of carbonate of lime (figs. 1 & 2). On breaking off fragments of these stones (often so hard as to defy a heavy geological hammer), the passages were found to extend in many cases to the depth of an inch, and in some cases to two inches and a half, the breadth of the cavity varying proportionately. The excavations in this case were not cylindrical, as with Sabella
, but in transverse section presented a keyhole- or figure-of-eight outline (fig. 3). As seen in the drawing, they do not terminate abruptly, but appear to be formed by the bending-round of a single cylindrical gallery. Within these galleries, and coiled round so that the head and the tail both point to the aperture, many specimens of the worm which made them were found (figs. 5, 6). The worm does not lie in immediate contact with the stone, but the interior of the gallery is lined and its substance impregnated with a viscid secretion derived from the worm's body. The partition between the two parallel passages of the gallery is often formed solely of this material. Boulders are not unfrequently found which have been entirely deserted by their occupants, or from which these have passed away by death and decay; and in those cases the animal matter which lines the excavated passages is very easily seen, and sometimes may be peeled off as a black carbonaceous film.
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