JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Marine Biological Laboratory is collaborating with JSTOR to digitize, preserve and extend access to Biological Bulletin.In 1817 Oken obtained fertile eggs from Lymnaea auricularis which were reared in isolation during their entire reproductive period. Baudelot (1863) reported both self-fertilization and cross-fertilization in Lymnaea. Pelseneer (1920) saw only one polar body extruded from the eggs of Lymnaea (three species), and concluded that reproduction in isolated snails was parthenogenetic. However, Colton, (1918) in L. columella and Crabb (1927a) in L. stagnalis observed two polar bodies and on the basis of their observations concluded that parthenogenesis did not occur. Colton further reported that, although self-fertilization did occur, crossfertilization was the rule; Crabb reported that cross-fertilization was mechanically impossible (1927b). Seshaiya (1927) concluded from a study of breeding habits of L. luteola that both cross-and self-fertilization occurred in this species. Lang in 1900 claimed that self-fertilization could occur without self-copulation, while Kunkel (1908) believed that self-copulation was indispensable to self-fertilization, basing his opinion in part on the observation of self-copulation in L. auricularis by Von Baer in 1835. Colton and Pennypacker (1934) reported that self-fertilization in L. columella for 93 generations did not decrease the viability of the strain. Boettger (1944), in his survey of the Basommatophora, concluded that self-and cross-fertilization were both common in this order. DeWitt (1954) found the percentage of hatching less in self-fertilized eggs of Physa gyrina than in cross-fertilized eggs.The first genetic proof that both self-and cross-fertilization occur in snails was supplied by Diver, Boycott and Garstang (1925) in a study of the inheritance of inverse symmetry in L. peregra. Further proof was obtained in the study of the inheritance of albinism in this snail (Boycott and Diver, 1927). Ikeda and Mura (1934), using shell color as a genetic marker, demonstrated that both self-and cross-fertilization occurred in the land snail, Bradybaena similaris.Bretschneider (1948a, 1948b) investigated the mechanism of insemination and oviposition in L. stagnalis. He reported that he had seen sperm balls leaving the seminal vesicle and being swept up the female tract to the hermaphroditic duct, where he assumed fertilization occurred. As additional evidence he reported seeing a complete spermatozoon inside the cytoplasm of an egg still in the duct.
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