vii MOLLUSCA LITERATURE 269 



pleurovisceral cords answer to the lateral trunks of the Platodes, 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 Molluscan organisation would be 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 musculature 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 

 simplified 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 jWorks. Investigations 

 treating of all or several Classes. 



Boll. Bcitrdge zur Vergleich. Histologie des Molluskentypus. Arch, filr mikr. Anat. 



Supplementband. 1869. 

 H. G. Bronn. Die Klassen und Ordnungen dcs Thierreiches. 3 Bd. Malacozoa. 



I. Malacozoa acepliala. 1862. II. Malacozoa cephalophora, von W. Keferstein. 



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

 G. Cuvier. Memoires pour servir a I'histoire et a I'anatomie des Mollusques. Paris, 



1817. 

 G. B. Deshayes. Traite elementaire de Conchyliologie. 3 vols. Paris, 1839-1857. 



Histoirc ii.<:itiirclle des Mollusques (Exploration de I'Algerie). 1848. 



Eydoux and Souleyet. Voyage autour du monde sur la corvette la Bonite. Histoirc 



ni't.tu relic. Zoologie. Paris, 1852. 

 Paul Fischer. Manuel de Conchyliologie et de Paleontologie conchylwloffique. His- 



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

 H. von Jhering. Vergleichende Anatomic des Nervensy stems, und Phylogenie der 



Mollusken. Leipzig, 1877. 



Keber. Beitrdge zur Anatomie und Physiologic der Weichthiere. Kb'nigsberg, 1851. 

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



1883. 



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

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

 Poll. Testacea utriusque Siciliae eorumque historia et anatorne. 3 Bd. 1791-1795. 



