vii MOLLUSC A LITERATURE 269 



pleurovisceral cords answer to the lateral trunks of the Platodcs, 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 Moll n sea 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 Turliellaria. 



Review of the most important Literature. 



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

 treating of all or several Classes. 



Boll. Beitrdge zur Vcrgleich. Histologie des Molluskentypus. Arch, fur mikr. Anat. 



Supplcmcntband. 1869. 

 H. G. Bronn. Die Kl,asscn und Ordnungcn dcs TJiicrreiches. 3 Bd. Malacosoa. 



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



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

 G. Cuvier. M&nwires pour servir a Fhistoirc et a I'anatomie dcs Mollusqucs. Paris, 



1817. 

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



Histoire naturelle des Mollusqucs (Exploration de I'Algfric). 1848. 

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



naturcllc. Zoologic. Paris, 1852. 



Paul Fischer. Manuel de Conchyliologic et de Paleontologie conchyliologique. His- 

 toire naturelle des Mollusqucs mvants ctfossiles. 2 vols. Paris, 1887. 

 H. von Jhering. Vcrgleichcndc Anatomic des Ncrvensystems, und Phylogenic der 



Molluskcn. Leipzig, 1877. 



Keber. Bcitragc zur Anatomic und Physiologic der Weichthicre. Kijnigsberg, 1851. 

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



1883. 



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

 Pelseneer. Introduction d I'etudc dcs Mollusqucs. Bruxelles, 1894. 

 Poli. Tcstacca utriusque Siciliae corumque historia ct anatome. 3 Bd. 1791-1795. 



