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 led to the loss of the radula, and is accompanied by the division of the shell into two valves. The peculiarities of the Gastropoda are all due to the torsion of the shell and body. The Cephalopoda can be derived without much difficulty from the schematic Mollusc, if we assume that some metameric repetition of organs has occurred, as explained above in reference to the coelom. The foot has been developed into long processes which have extended in a circle round the mouth; all the ganglia, including the visceral, have been concentrated around the oesophagus.

Habits and Distribution.—More than 28,000 species of living Molluscs have been distinguished, of which more than half are Gastropods. They are essentially aquatic animals, and the majority live in the sea. Some, like many Cephalopods and the Pteropods, are pelagic or free-swimming; others creep or lie on the sea bottom. Some are littoral, living between tide-marks; others are found at very various depths, up to 2800 fathoms. A few species have invaded the fresh waters, while the pulmonate and terrestrial Gastropods are distributed over the whole surface of the land in all latitudes and to a height of 15,000 ft. As a rule Molluscs are free and more or less active, but many Lamellibranchs are sedentary, and a few of these and of Gastropods are permanently fixed to their habitat. Commensalism occurs in a few instances, but parasitism either external or internal is rare. The latter is confined to certain Gastropods which live in Echinoderms and are extremely degenerate in structure. Protective resemblance is exhibited by some Nudibranch Gastropods which have assumed the colour and appearance of their habitat.

.—I. Morphology. (1) G. Cuvier, Mémoires pour servir à l'histoire et à l'anatomie des mollusques (Paris, 1816). (2) J. Poli, Testacea utriusque Siciliae, eorumque historia et anatomia, tabulis aeneis 49 illustrata, vols. i.–iii., fol. (Parma, 1791–1795 and 1826–1827). (3) St delle Chiaje, Memorie sulla storia e anatomia degli animali senza vertebre del regno di Napoli (Naples, 1823–1829), new edition

with 172 plates, fol., 1843. (4) J. Vaughan Thompson, Zoological Researches (Cork, 1830); memoir iv., “On the Cirripedes or Barnacles, demonstrating their deceptive character.” (5) A. Kowalewsky, “ Entwickelungsgeschichte der einfachen Ascidien,” in ''Mém. de'' ''l'acad. des sciences de St Petersbourg'' (1866), and “Entwickelungsgeschichte des Amphioxus lanceolatus,” ibid. (1867). (6) J. Vaughan Thompson, Zoological Researches (Cork, 1830); memoir v., “Polyzoa, a new animal discovered as an inhabitant of some Zoophytes.” (7) C. G. Ehrenberg, “Die Korallenthiere des Rothen Meeres” (Berlin, 1834); ''Abhand. d. k. Akad. d. Wissenschaften in Berlin'' (1832). (8) H. Milne-Edwards, Recherches sur les polypiers de France (Paris, 1841–1844). (9) H. Milne-Edwards, papers in the Annales des sciences naturelles (1841–1860). (10) H. de Lacaze-Duthiers, papers in the Annales des sciences naturelles, e.g. “Anomia” (1854), “Mytilus” (1856), “Dentalium” (1856–1857), “Purpura” (1859), “Haliotis” (1859), “Vermetus” (1860). (11) A. Kölliker, Entwickelungsgeschichte der Cephalopoden (Zürich, 1844). (12) C. G. Gegenbaur, Untersuchungen über Pteropoden und Heteropoden, (Leipzig, 1855). (13) J. W. Spengel, “Die Geruchsorgane und das Nervensystem der Mollusken,” ''Zeitschr. f. wiss. Zool.'' (1881). (14) Richard Owen, Memoir on the Pearly Nautilus (London, 1832). (15) L. Cuenot, “Excretion chez les mollusques,” ''Arch. d. biol.'' XVI. (1899). (16) P. Geddes, “On the Mechanism of the Odontophore in certain Mollusca.” (17) T. H. Huxley, “On the Morphology of the Cephalous Mollusca,” ''Phil. Trans.'' (1853). (18) Von Jhering, Vergleichende Anatomie des Nervensystems und Phylogenie der Mollusken (Leipzig, 1877). (19) E. R. Lankester, “Contributions to the Developmental History of the Mollusca,” ''Phil. Trans.'' (1875); “Note on the Coelom and Vascular System of Mollusca and Arthropoda,” ''Quart. Journ.'' ''Micr. Sci.'' XXXIV. (1893). (20) P. Pelseneer, Introduction à l'étude des Mollusques (Brussels, 1894); “Recherches sur les Mollusques archaiques,” ''Mem. cour. Acad. belg.'', LVII. (1899); “Mollusca,” Lankester’s Treatise on Zoology, pt. v. (1906).

II. Conchology.—(21) Cooke, “Molluscs,” Cambridge Natural History, vol. iii. (1895). (22) Fischer, Manuel de conchyliologie (1887). (23) Jeffreys, British Conchology (1862–1869). (24) Simroth, “Mollusca,” Bronn’s Klassen und Ordnungen des Thierreichs, Bd. iii. (1895), in prog. (25) Tryon, Manual of Conchology (1878), in prog. (26) Woodward, A Manual of the Mollusca (1880).

 MOLLUSCOIDA, a name long employed to denote a division of the animal kingdom which contained (q.v.), ' (q.v.), and ' (q.v.), the members of the three groups having been supposed to resemble the Mollusca. As it is now known that these groups have no relation to molluscs, and very little to one another, the name Molluscoida has been abandoned.  MOLLY MAGUIRES, an Irish American secret society which maintained numerous branches in the anthracite coal regions of Pennsylvania, U.S.A., from 1854 to 1877, and perhaps later. The name was imported from Ireland, where it had been used to designate one of the Ribbon societies that devoted its energies to intimidating and maltreating process servers and the agents of landlords, and whose greatest activity was between 1835 and 1855. The Irish society of Molly Maguires seems to have been organized in 1843 in the barony of Farney, Co. Monaghan, to co-operate with the ribbonmen, and its membership seems to have been confined to the very lowest classes. The Molly Maguires of Pennsylvania consisted of similar classes of Irishmen, but there seems to have been no connexion between the two societies. Every member of the American organization was also a member of the Ancient Order of Hibernians, an association organized for benevolent purposes, and having branches throughout the United States and Great Britain. To the Ancient Order of Hibernians none might be admitted but persons of Irish birth or descent, who were Roman Catholics, and whose parents were Roman Catholics; but notwithstanding this requirement, the organization—being a secret society—was under the ban of the Catholic Church. At the head of each division or lodge there was a “body master,” who communicated directly with a county delegate; the county delegates reported to the state delegate, and the state delegates to a national delegate. The supervision of the whole order was vested in a “Board of Erin,” meeting quarterly in England, Ireland or Scotland, and at each meeting arranging a new code of signals and passwords, which were communicated to the national delegate in the United States by the steward of a transatlantic steamship, and thence were transmitted to the various subdivisions. In the mining districts of Pennsylvania the organization fell under the control of a lawless element,