record. M. de Quatrefages pressed specimens of an Eolis between the compressor until the skin was ruptured and the body, nearly emptied of its sarcode, was flattened almost to a membrane; yet on being replaced in sea-water these individuals recovered perfectly. And of the Tunicata, we are told that "not unfrequently we find Salpæ making their way through the waters deprived of their nuclei by birds or fishes, retaining their vitality for a considerable time, and exercising their muscular powers when the organs of digestion, circulation, and reproduction have been torn away." † 66 The singular power the Mollusca have of reproducing organs which have been amputated was first determined by the Abbé Spallanzani, who too often experimented without a definite object in view, for the sake merely of satisfying a cruel curiosity as to the result. He took snails (Helix pomatia, nemoralis, and lucorum), and cut away the tentacula either in part or wholly, and they were renewed in about two months' time, perfect in all respects even to the restoration of the eyes at their tips, with all its humours and coats in their original integrity. "The snail," says Spallanzani, makes the same use of the new horns as it did of the old, whether by protruding them from the head, extending, contracting, or concealing them, or by displaying their acute and lively sensibility; so that on the most gentle touch, they are suddenly withdrawn and put in safety."+ If the experiment is carried further, and the half or the whole head amputated, the regeneration of the parts is equally complete, a longer time being allowed for the redintegration; and you cannot reflect on this fact without wonder, for in the head of this creature are placed its organs of sense, the eye, the ear, and the feelers; the brain, the centre of its nervous system; the mouth and its various appendages, and a large mass of muscles; yet all these organs grow again to such perfection that they cannot be distinguished from the original formations! All the circumstances requisite for the success of the experiment are not well known. If adroitly conducted success in general follows; but under apparently the same circumstances the shortly after they had been frozen."- Ray Reports on Zoology, 1847, p. 216. * Ann. des Sc. Nat. (1843) xix. 278 and 311. Forbes and Hanley, Brit. Mollusca, i. 47. Tracts on the Nat. Hist. of Animals and Vegetables, translated by J. G. Dalyell, ii. 228. I refer to this volume for a very complete history of Animal Reproductions. experiment often fails, and the mutilated animal may be kept years in vain expectation of witnessing "this admirable reproduction." A sufficient degree of heat is essential to the, success. Temperate is not enough; and the heat must be at least 61°. The experiments of Spallanzani, made principally during the spring and summer of 1766, raised curiosity to a high pitch, and led to a very general decapitation of the snail race. The results were confirmed by M. Bonnet, M. Tissot, Father Barletti, H. Roos, M. Lavoisier, Turgot, Tenon, Herissant, Müller, Scarella, Schoeffer, Abbé Troilo, Senebier, and by Signor Caldani, Girardi, and Pratalongo; and their accuracy was denied by M. Wartel, Father Cotté, M. Valmont de Bomare, Argenville, Schroeter, Murray, Adanson, and Presciani. Adanson's opinion was given with characteristic confidence: "I have," he said, "as every one has had, reproductions, even very immediate ones, of horns, heads, lips, and other parts; but these were reproductions of parts that had not been entirely cut off: for all the heads, I say, the real heads, all the horns, all the jaws, and the other parts which have been completely cut away, and only a quarter of a line from the origin, never exhibited any kind of reproduction, far less a complete regeneration. Let us be strict, and investigate the truth. All who have mutilated snails, and first Sig. Spallanzani, have certainly been deceived. They have thought the head was severed when the cap only has been cut off: they have believed that they separated or eradicated the horns and jaws, while the origin always remained; whence it is not wonderful if reproductions ensued. These, you will candidly admit, are not reproductions, or rather regenerations, such as you, Trembley and Reaumur, had seen in fresh-water worms, the polypus, the claws of lobsters.-How many well-credited operations have deceived persons, less familiar than us, with similar operations and the anatomy of shelled animals. They have thought that they had completely cut off so many heads, horns, and mouths, beyond the origin, which in every journal and periodical paper, they have so liberally regenerated. I am well aware of our deficiency in most nice experiments; and, notwithstanding my great experience, I may almost presume to say, dexterity in the anatomy of the smallest animals, I always distrust myself. For this reason I have repeated the same experiments an hundred and an hundred times before hazarding the results before the public." But neither this strong denial, nor other counter-evidence, can rebut the positive experiments of Spallanzani; and the very boldest of his statements,-the renewal of the entire head,-has been even established by naturalists in the fullest manner, for it is not true, as Bosc and others would have us to believe, that "the animal infallibly dies when the first ganglion, which essentially constitutes the head, has been taken away." * In 1808, M. Tarenne decapitated many snails, and proved, by careful dissection, that the amputated portion contained not only the tentacula, the jaw, and the upper lip, but the brain likewise, and the anterior part of the foot, yet these maimed individuals reproduced the head complete at the end of one year or more. new head only differs from the old by having a paler and smoother skin; and sometimes a sort of furrow marked its junction with the trunk.† The It is not, as Spallanzani ascertained, every kind of snail (Helix), which possesses the power in question; nor is the power limited to that family of Mollusks. From a very early date in the history of animals, it has been affirmed that the Cuttle-fish could renew their amputated limbs ; and the snail of the beautiful Harp-shells (Harpa) reproduces its foot. This member is so disproportionably large that it cannot be drawn within the shell in extraordinary circumstances, so that when attacked by an enemy the Mollusk, by pressing the foot firmly against the sharp lip of the shell, voluntarily cuts away the hinder portion, and thus secures its safety by the loss of its limb. In two or three species of pectinibranchial zoophagous Mollusca Madame Power proved the reproductive agency in them by direct experiment. She lopt off the tentaculum with the eye from a Triton nodiferum, and at the end of twenty days a new tentaculum had grown six lines in length," that which had been cut off measured fourteen lines.' A Murex trunculus reproduced the head and tentacula, and the operculum, which had been purposely torn away; and a Conus its tentacula and respiratory siphon. § The foot of the Mussel (Mytilus edulis) being cut off will be renewed. The diseases of the Mollusca are scarcely known; and all the accurate information we possess is limited to their parasites. Of terrestrial Mollusca, Reaumur has described in detail a sort of mite which infests the Helicidæ or Snails of France. It is found in numbers on them in dry weather, but rarely in rainy seasons, for the viscid secretion of the snail being then abundant seems to destroy the parasites. *Griffith's Cuvier, part xxxix. p. 329. Bosc. Vers. i. 89. + Bowdich's Man. of Conchology, i. 75. Rang's Manual, p. 211. § Charlesworth's Mag. N. Hist. ii. 64. Having collected some snails in a wet season no mites could be discovered on them; but placing them in jars to exclude the moisture, their acaridan pests were seen upon them after the lapse of some time, varying from five or six days to three weeks. Reaumur has counted upwards of twenty mites on the same snail; and he tells us they are rarely seen at rest, but are almost always creeping about, which they do with extreme quickness. They are usually noticed near the collar of the snail on the exterior of the body, but Reaumur believes they are there by accident, and that their natural place is within the intestine. The mites, he says, are continually on the watch to enter the vent whenever the snail has occasion to open this aperture; and it is no sooner opened than they rush in and walk quickly up the canal. The reason that we find them on the surface is this,-they are pushed out of the intestine along with the excrements, and they must remain on the surface until a favourable opportunity presents itself for their re-entrance. In Cyclostoma elegans, Reaumur found acari in the very middle of the intestinal canal.* The Rev. Leonard Jenyns has found the same mite (Philodromus limacum) on some of our English slugs (Limax variegatus and Arion empiricorum); and his observations respecting it agree generally with those of Reaumur. But he differs from the great French naturalist in believing that the natural habitat of the mite is the pulmonary cavity, and not the intestine. "I am inclined to think," he writes, "that this cavity is its principal residence, whence it only comes forth occasionally to ramble upon the surface of the body. In one instance, I confined in a close box a slug which, to all appearance, was free from parasites. On opening the box a day or two afterwards, I observed very many crawling about the slug externally, all of which would seem to have proceeded from the pulmonary cavity. On another occasion I observed these insects running in and out of this cavity at pleasure; and some which I saw retire into it never re-appeared, although I watched the slug narrowly for a considerable time. It is remarkable, as Dr. Shaw observes, that the slug appears to suffer no particular inconvenience from these parasites, and even allows them to run in and out of the lateral orifice without betraying the slightest symptoms of irritation." In England the mite seems to have been found on slugs only; in France it infests slugs and *Hist. de l'Acad. Roy. des Sc. for 1710, p. 414. snails indifferently; but in Scotland I have never seen it on either tribe-enjoying there a joke-provoking immunity. -Two or three different mites are born to plague even the fresh-water mussels, by crawling with their spinous feet over the cloak of the animal, or hiding between the layers of its delicate gills. Hydrachna concharum of M. Bäer, which may be identical with the Limnocharis anodontæ of Pfeiffer, and the Trombidium notatum of Rathke, thus fret the Unio pictorum and the Anodontæ. † These mites have not yet been discovered in this country. The lacustrine Gasteropods are greatly vexed with the parasitism of a worm that has been loosely referred to the genus Gordius (G. inquilinus, Müll.), and which Draparnaud erroneously identifies with the Nais vermicularis.Müller says that the worm resembles in every respect the tentaculum of a Planorbis. It attaches itself to any exposed part of the skin, but prefers a station between the collar and the neck of the snail, where several may be noticed with one end fixed in the flesh, while the other is ever moving with a sort of painful twisting and twining motionpainful because it reminds one of the worm that never dieth. The ill they occasion is of uncertain nature; and probably there are more than one species, for it is not likely that the parasite of the fluviatile Mollusca of Europe is identical with that of those of the New World. After describing the Physa heterostropha of the United States, Dr. Gould says: "On looking carefully about the neck of the animal of this shell, we find him beset with numerous little things looking like short, minute, white lines, which are, in truth, little parasites (Gordius inquilinus, Müll.), attached like leeches, and which derive their nourishment from the fluids of the animal, without his having the power to dislodge them." S I The leech-like form of this parasite reminds me of another which you may occasionally find in the shells of Bivalves, lurking between the branchial leaflets. This is the Hirudo grossa of Müller, who found it in the Artemis exoleta. have found it frequently in Cyprina islandica, and once in Cardium echinatum; and although I could not detect a consumption in the fish, yet from the character and relationship *Loudon's Mag. Nat Hist. v. 697. + Bull. des Sc. Nat. Fev. 1829, p. 295. Verm. Terr. et Fluv. Hist. ii. 33.-Draparnaud mistook the worms for a kind of trachea, whose function it was to separate the air from the surrounding water. Hist. des Mollusques, 49. § Invert. of Massachusetts, 213. |