Production of Musical and other Sounds.—Certain molluscs are said to be capable of producing musical sounds. Sir J. E. Tennent describes his visit to a brackish-water lake at Batticaloa, in Ceylon, where the fishermen give the name of the ‘crying shell’ to the animal supposed to produce the sounds. “The sounds,” he says,[117] “came up from the water like the gentle thrills of a musical chord, or the faint vibrations of a wineglass when its rim is rubbed by a moistened finger. It was not one sustained note, but a multitude of tiny sounds, each clear and distinct in itself; the sweetest treble mingling with the lowest bass. On applying the ear to the woodwork of the boat, the vibration was greatly increased in volume. The sounds varied considerably at different points as we moved across the lake, and occasionally we rowed out of hearing of them altogether.” According to the fishermen, the shells were Pyrazus palustris and Littorina laevis. It appears uncertain whether the sounds are really due to Mollusca. Fishermen in other parts of India assert that the sounds are made by fish, and, like those in Ceylon, produce the fish which they say ‘sings.’ The same, or a similar sound, has also been noticed to issue from the water in certain parts of Chili, and on the northern shores of the Gulf of Mexico. Dendronotus arborescens, when confined in a glass jar of sea water, has been noticed[118] to emit a sound like the clink of a steel wire. According to Lieut.-Col. Portlock,[119] F.R.S., Helix aperta, a very common species in South Europe, has the property of emitting sounds when irritated. When at Corfu, he noticed that if the animal is irritated by a touch with a piece of straw or other light material, it emits a noise, as if grumbling at being disturbed. He kept a specimen in his house for a considerable time, which would make this noise whenever it was touched.

The Rev. H. G. Barnacle describes the musical properties of Achatinella in the following terms:[120] “When up the mountains of Oahu I heard the grandest but wildest music, as from hundreds of Aeolian harps, wafted to me on the breezes, and my companion (a native) told me it came from, as he called them, the singing shells. It was sublime. I could not believe it, but a tree close at hand proved it. On it were many of the Achatinella, the animals drawing after them their shells, which grated against the wood and so caused a sound; the multitude of sounds produced the fanciful music. On this one tree I took 70 shells of all varieties.”

Habits of the Agnatha.—Not much is known of the habits and mode of life of the Agnatha, or carnivorous Land Mollusca. In this country we have only two, or at most three, of this group, belonging to the genus Testacella, and, in all probability, not indigenous to our shores. There seems little doubt, when all the circumstances of their discovery are taken into account, that both Testacella haliotidea and T. Maugei have been imported, perhaps from Spain or Portugal in the first instance, along with roots imbedded in foreign earth, for their earliest appearances can almost invariably be traced back to the neighbourhood of large nursery grounds, or else to gardens supplied directly from such establishments.

The underground life of Testacella makes observation of its habits difficult. It is believed to feed exclusively on earthworms, which it pursues in their burrows. Continued wet weather drives it to the surface, for though loving damp soil it is decidedly averse to too much moisture, and under such circumstances it has even been noticed[121] in considerable numbers crawling over a low wall. In the spring and autumn months, according to Lacaze-Duthiers,[122] it comes to the surface at night, hiding itself under stones and débris during the day. Earthworms are, at these periods, nearer the surface, and the Testacella has been seen creeping down into their burrows. The author has taken T. Maugei abundantly under clumps of the common white pink in very wet weather, lying in a sort of open nest in the moist earth. On the other hand, when the earth is baked dry by continued drought, they either bury themselves deeper, sometimes at a depth of 3 feet, in the ground, or else become encysted in a capsule of hardened mucus to prevent evaporation from the skin. When first taken from the earth and placed in a box, the Testacella invariably resents its capture by spitting up the contents of its stomach in the shape of long fragments of half-digested worms.

It appears not to bite the worm up before swallowing it, but contrives, in the most remarkable manner, to take down whole worms apparently much too large for its stomach. Mr. Butterell relates[123] that, after teasing a specimen of T. Maugei, and making it emit a quantity of frothy mucus from the respiratory aperture, he procured a worm of about three inches long, and rubbed the worm gently across the head of the Testacella. The tongue was rapidly extended, and the victim seized. The odontophore was then withdrawn, carrying with it the struggling worm, which made every effort to escape, but in vain; in about five minutes all had disappeared except the head, which was rejected. This protrusion of the tongue (radula) and indeed of the whole pharynx, is a very remarkable feature in the habits of the animal. It appears, as it were, to harpoon its prey by a rapid thrust, and when the victim is once pierced by a few of the powerful sickle-shaped teeth (compare chap. viii.) it is slowly but surely drawn into the oesophagus (Fig. 20).

Most gardeners are entirely ignorant of the character of Testacella, and confuse it, if they happen to notice it at all, with the common enemies of their tender nurslings. Cases have been known, however, when an intelligent gardener has kept specimens on purpose to kill worms in ferneries or conservatories. In some districts these slugs are very numerous; Lacaze-Duthiers once dug 182 specimens from a good well-manured piece of ground whose surface measured only ten square yards.

Towards the end of September or beginning of October the period of hibernation begins. I infer this from the behaviour of specimens kept in captivity, which, for about a fortnight before this time, gorged themselves inordinately on as many worms as I chose to put into their box, and then suddenly refused food, buried themselves deeply in the earth, and appeared no more during the winter. The eggs are apparently much less numerous than is the case with Limax or Helix, and very large, measuring about ⅙ inch in diameter. They are enveloped in a remarkably tough and elastic membrane, and, if dropped upon any hard surface, rebound several inches, just like an india-rubber ball.

The animal creeps rather rapidly, and has the power of elongating its body to a remarkable extent. When placed on the surface of the ground, in the full light of day, it soon betrays uneasiness, and endeavours to creep into concealment. Its method of burying itself is very interesting to watch. It first elongates its neck and inserts its head into the soil; gradually the body begins to follow, while the tail tilts upwards into the air. No surface motion of the skin, no writhing or wriggling motion of any kind occurs; the creature simply works its way down in a stealthy and mysterious way, until at last it is lost to view.

The great Glandina, which attain their maximum development in Mexico and the southern United States, are a very noticeable family in this group. According to Mr. Binney,[124] Glandina truncata Gmel., one of the commonest species of the genus, is somewhat aquatic in its habits. It is found in the sea islands of Georgia and around the keys and everglades of Florida, where it attains a maximum length of 4 inches, while in less humid situations it scarcely measures more than 1 inch. It occurs most abundantly in the centre of clumps and tussocks of coarse grass in marshes close to the sea-coast. By the action of the sharp, sickle-shaped teeth of its radula the soft parts of its prey (which consists chiefly of living Helices) are rapidly rasped away; sometimes they are swallowed whole. It has been known to attack Limax when confined in the same box, rasping off large pieces of the integument. In one case an individual was noticed to devour one of its own species, thrusting its long neck into the interior of the shell, and removing all the viscera.

The Glandinae of southern Europe, although scarcely rivalling those of Central America in size or beauty, possess similar carnivorous propensities. Glandina Poireti has been observed,[125] on Veglia Island, attacking a living Cyclostoma elegans. By its powerful teeth it filed through two or three whorls of the shell of its victim, and then proceeded to devour it, exactly in the same manner as a Natica or Buccinum perforates the shell of a Tellina or Mactra in order to get at its contents.

Few observations appear to have been made on the habits or food of Streptaxis, Rhytida, Ennea, Daudebardia, Paryphanta, and other carnivorous Mollusca. A specimen of Ennea sulcata, enclosed in the same box as a Madagascar Helix (sepulchralis Fér.) many times its own size, completely emptied the shell of its inhabitant.[126] Mr. E. L. Layard informs me that certain Cape Rhytida, e.g. R. capsula Bens., R. dumeticola Bens., and R. vernicosa Kr., eat Cyclostoma affine, Helix capensis, H. cotyledonis, etc. To Mr. Layard I am also indebted for the—perhaps apocryphal—tradition that the best time to capture the great Aerope caffra Fér. in numbers was after an engagement between the Kaffirs and Zulus, when they might be observed streaming from all points of the compass towards the field of slaughter. The Cuban Oleacina are known to secrete a very bitter fluid which they emit; this perhaps produces a poisoning or benumbing effect upon their victims when seized. They devour operculates, e.g. Helicina regina and sagraiana.[127]