400 THE KEYHOLE LIMPET. 



communicates its color to paper, and may be conveniently used as a blue ink ; several 

 memoranda and pages of my journal, written with this fluid, have, after a lapse of more 

 than five years, retained their original appearance both in color and intenseness. For 

 this use, however, it must be employed from the recent animal, as it will not keep in 

 any quantity, but becomes thin and discolored. 



It is believed that this fluid is analogous in use to the black secretion which the 

 cuttle-fish pours forth to obscure the water and elude the pursuit of its enemies ; but 

 this opinion must be received with some qualification. The living examples of Janthina 

 which I have irritated when they have been confined in a vessel containing sea-water 

 have not emitted any of the colored fluid ; when taken in hand, they would sometimes 

 allow a little to exude ; but the entire quantity obtained from one animal by artificial 

 means was never sufficient to cloud or obscure, although it would stain about half a 

 pint of pure water." 



When attached to the living animal, the shell is covered with a delicate and rather 

 slippery membrane, and the violet hue possesses a peculiar liveliness, which soon 

 vanishes after the death of the inhabitant. The raft is delicate white. Its length is 

 about one inch, and the shell is very similar in shape and dimensions to that of our 

 common garden-snail. 



THE well-known univalves, so familiar under the name of Limpets, are divided into 

 several families, on account of certain variations in the structure of the shell. The 

 first family is termed Fissurellidae, on account of the fissure which appears either at the 

 apex or in the front edge of the shell. 



All the Limpets are strongly adhesive to rocks, as is well known by every one who 

 has tried to remove one of these molluscs from the stony surface to which they cling. 

 The means by which the animal is able to attach itself with such firmness is analogous 

 to the mode in which the suckers of the cuttle-fish adhere to the objects which they 

 seize, the formation of a vacuum, and the consequent pressure of the atmosphere, being 

 the means employed. The foot of the Limpet is rounded, broad, thick, and powerful ; 

 and when the animal wishes to cling tightly to any substance, it presses the foot firmly 

 upon the surface, and retracts its centre, while its edges remain affixed to the rock. A 

 partial vacuum is therefore formed, and the creature becomes as strongly attached to 

 the rock as a boy's leathern sucker to the stone on which he has pressed it. 



The Limpets, although inactive and comparatively stationary, are able to glide slowly 

 by means of the foot, and leave very curious tracks in their progress. In the course 

 of long adhesion to a single spot, the animal works a slight hollow, into which the 

 edges of the shell sink when the creature is alarmed and presses itself to the rock, and 

 thus protects itself very effectually from being dislodged by the insertion of an animate 

 or inanimate lever under the shell. Several sea birds, and one or two of the land birds, 

 are in the habit of feeding on Limpets, which they dislodge by the simple process of 

 driving their sharp beak between the shell and the rock before the mollusc takes the 

 alarm and presses itself against the stoue to be moved. When the Limpet is quite at 

 ease, it has a custom of relaxing the foot and raising the shell from the rock, and at 

 such times it may be detached even by a quick stroke with the finger. 



Most, if not all, of the Limpets are edible, and can be eaten either cooked or in a 

 fresh state as they come off the rocks. Shipwrecked mariners have frequently saved 

 themselves from perishing with hunger by gathering the Limpets from the rocks on 

 which the vessel was cast away ; and I have made many a luncheon on these creatures 

 when engaged in searching the shores, and when time has been too precious to be 

 wasted in leaving the spot for refreshment. An empty shell of the mussel forms an 

 admirable spoon for the extemporized banquet. 



The KEYHOLE LIMPET is so called on account of the aperture at the top of the shell, 

 which serves as a passage through which is expelled the water that has passed over the 

 gills. This aperture is found in all the species of the genus Fissurrella, but varies greatly 

 in form and comparative dimensions, being, in some cases, a mere rounded hole in 



