| OCR Text |
Show 1897.J MR. W. E. C0LLINGE ON EUROPEAN SLUGS. 447 or striped, excepting in young specimens. Mantle large. Adult never keeled. Free-oviduct of moderate length, with its terminal portion usually globose or expanded. Sperm-duct usually, but not always, opens into the vestibule by a thickened ring-like swelling. Retractor muscle of the free-oviduct always situated above the lower portion, and joins with that supplying the receptaculum seminis. 2. THE Arion subfuscus GROUP. Usually banded, variable in colour. Varies in size from 35 to 75 millim. Mantle rather large. Adult never keeled. Free-oviduct generally sac-like or wide and long, without well-defined terminal swelling. Duct of receptaculum seminis usually long. Retractor muscles of the free-oviduct and receptaculum seminis usually distinct or only slenderly united. 3. THE Arion hortensls GROUP. Nearly always banded, of dark colour. Varies in size from 30 to 55 millim. Mantle medium-sized, often small. Adult never keeled. Sperm-duct usually long and tapering, passing imperceptibly into the vas deferens. Free-oviduct gradually tapering. Retractor muscles usually united, but only slenderly. 4. THE Arion fasciatus GROUP. Nearly always banded. In external appearance agrees very closely wdth the preceding group. Body sometimes keeled. Head of receptaculum seminis elongated, duct short. 5. THE Arion Intermedius GROUP. Animal usually of small size, varying from 15 to 27 millim. Mantle almost circular. Adult never keeled. Receptacular duct short and broad. Lessona and Pollonera (14) are wrong in stating, as one of the characters of the genus, that the penis ( = sperm-duct) and vas deferens are quite distinct, and do not pass imperceptibly into one another as in Ariunculus, for in numerous species there is no marked difference between the two. The term penis cannot be used for the male organ in this genus ; as has been pointed out by Simroth, it is not evertible, and bas no retraotor muscle, its function being for the storage of the spermatozoa. The free-oviduct assumes the function of the penis in this genus. It is evertible and provided with a retractor muscle. Messrs. Pilsbry and Vanatta (18) have suggested the term eplphallus for what I term sperm-duct, and vagina for what I term free-oviduct. I think it preferable, however, to retain the term epiphallus for the terminal portion of the vas deferens above the sperm-duct; the term vagina is not applicable to the genus Arion. 30* |
