VII M0LLU8GA— LITERATURE 269 



pleurovisoeral cords answer to the lateral trunks of the Plciiodes, and the pedal 

 cords to the ventral longitudinal trunks of the latter. If such a hypothetical racial 

 form were to secrete a dorsal shell, perhaps at first in the form of a thick cuticle 

 containing calcareous particles, a typical Mollusoan organisation would he produced. 

 The development of a shell would deprive the greater part of the surface of the body 

 of its original respiratory function, and would lead to the formation of localised 

 gills. By means of the development of a mantle fold these delicate-skinned organs 

 could be brought under the protection of the shell. The musculature on the dorsal 

 side, which the shell covered, would disappear, and with it the dorsal longitudinal 

 nerve trunks. The musculature on the ventral side, which was already strongly 

 developed in the Planaria, would become strengthened in the development of the 

 foot with its sole for creeping. A part of the dorsoventral muscnlature would be 

 changed into the shell muscle. 



In this derivation of the Mollusca their characteristic larval form might be 

 explained, without any need for tracing it to the Annelidan Trocophora, in the 

 following way. It would correspond to a Turbellarian larva (Miiller's Polyclade 

 larva, etc. ), on to which certain Molluscan characteristics such as the shell gland, 

 the shell, the anus, and the foot had been shifted back. The preoral ciliated band 

 (the velum) of the Molluscan larva would correspond with the same structure in 

 the Turbellarian larva. The primitive kidney of the former would answer to a 

 sijnplified water vascular system, while the permanent nephridia as ovarial and 

 seminal ducts might be homologised morphologically with the ducts of the 

 genital products in the Turbellaria. 



Review of the most important Literature. 



Comprehensive Works. Text-Books. General, Works. Investigations 

 treating of all or several Classes. 



Boll. Bcitrdge zur Vcrgleich. Histologic des Molhiskerdypus. Arch, fur mikr. Anat. 



Supplmnentbaiid. 1869. 

 H. G. Bronn. Die Klassen und Ordnmigen des Thierreichcs. 3 Bd. Malacozoa. 



I. Malacozoa acephala. 1862. II. Malacozoa ceplialophora, von W. Kcfcrstcin. 



1862-1866. (New edition now appearing, i. Simroth.) 

 G. Cuvier. Mimoires pour scrvir d, Vhistoirc et d V anatomic des Mollnsqucs. Paris, 



1817. 

 G. B. Deshayes. Traiti elimentaire de Conchyliologie. 3 vols. Paris, 1839-1867. 



Histoire naturelle des MoUusqucs {Exploration de V Ahjirie). 1848. 



Eydoux and Souleyet. Voyage autour du monde sur la corvette la Bonitc. Histoire 



naturelle. Zoologie. Paris, 1852. 

 Paul Fischer. Manuel de Conchyliologie et de Paliontologie emuhyliologique. His- 

 toire naturelle des Mollusques vivants ctfossiles. 2 vols. Paris, 1887. 

 H. von Jhering. Verglcichende Anatomic des JHervcnsy stems, und Phylogenie der 



Mollusken. Leipzig, 1877. 

 Keber. Bcitrdge zitr Anatomie und Physiologic der Weichthicre. Konigsberg, 1851. 

 E. Ray Lankester. Mollusca. Encyclopaedia Britannica. 9th edit. Vol. XVI. 



1883. 

 R. Leuckart. Zoologische Untersuchungen. Heft 3. Giessen, 1854. 

 Pelseneer. Introduction d I'itucle des Mollusques, Bruxelles, 1894. 

 Poll. Testacea utriusque Sieiliae eorumque historia et anatome. 3 Bd. 1791-1795. 



