CHAPTEE X. 



PHYLUM MOLLUSCA.* 



Bilaterally symmetrical unsegmented animals, with a ventral foot, 

 and usually with a radula, a mantle fold, and a univalve or bivalve 

 calcareous shell. The central nervous system consists of a circum- 

 oesopliageal ring with various ganglionic developments, and both the 

 haemoeoel and coelom contribute to the formation of the perivisceral 

 cavities. 



The group Mollusca\ with somewhat of its present limits was 

 established by Cuvier (1798). Linnaeus had used the word before, 

 but his group Mollusca bore very little resemblance to that of Cuvier, 

 and even Cuvier himself included in the " embranchement " a number 

 of forms which are now known to have nothing to do with it. 

 Cuvier's Mollusca included the Cephalopoda, the Gastropoda, the 

 Pteropoda, the Acephala, and the folloAving groups now removed 

 from them : the Bracltiopoda, the Tunicata, and the Cirripedia. 



In many points the Mollusca resemble the Annelida, with which 

 phylum they are clearly closely allied. The arrangement of the 



* J. Poli, "Testacea utriusque Siciliae, eorumque liistoria et anatome," 3 vols., 

 Parma, 1791-1795. G. Cuvier, Mhnoires pour scrvir a I'histoire et a I 'anatomic 

 des Mollusques, Paris, 1817. G. B. Deshayes, "Histoire naturdU dcs Mollusques 

 (Exploration de I' Algerie)," Paris, 1844-48. R. Leuckart, " Ueb. d. Morphologic, 

 it. d. Verwand. VerMlt. der Wirbcllosen Thiere," Braunschweig, 1848. Eydoux 

 and Souleyet, "Voyage autour du monde sur la corvette la Bonite. Histoire naturellc 

 Zoologie" Paris, 1852. T. H. Huxley, "On the Morphology of the Cephalous 

 Mollusca as illustrated by the Anatomy of certain Heteropocla and Pteropoda, etc. ," 

 Phil. Trans., 1853. Bronn and Keferstein, "Die Klassen u. Ordnungen der Weich- 

 thierc," Leipzig and Heidelberg, 1862-66. E. Ray Lankester, "Contributions 

 to the developmental history of the Mollusca," Phil, jkrans., 1875. P. Fischer, 

 "Manual de Conchyliologie et de Paleontologic conchyliologiquc, Histoire nat. des 

 Mollusqucs vivants ctfossiles," 2 vols., Paris, 1887. P. Pelseneer, "Introduction 

 a 1' etude des Mollusques," Bruxelles, 1894. K. A. Zittel, Handbuch der Palaeon- 

 tologic, Abth. 1, Palaeozoologie, Bd. 2, Mollusca and Arthropoda, Munich and 

 Leipzig, 1881-85. S. P. Woodward, A Manual of the Mollusca, 3rd Ed., London, 



t For a short literary history of the Mollusca, vide E. Ray Lankester's Article 

 on Mollusca in the last edition of the Encyclopaedia Britannica, and republished 

 in " Zoological Articles," London, 1891. 



