REPRODUCTIVE SYSTEM AND SEXUAL SUCCESSION OF L. BULIMOIDES 187 



other limb of the mucous gland is a plump, horseshoe shaped crescent of glandular tissue (MUC.AC.) 

 closest on the right side to the edge of the mantle cavity and the columellar muscle (COL.). Sperm 

 would not appear to enter this part of the mucous gland and it forms an appendage to a deeper lying 

 part of the genital duct. This deeper portion constitutes the albumen gland (ALB.), which consists of 

 a wide atrium, thinner walled than the mucous gland. The non-glandular little hermaphrodite duct 

 (L.HERM.) opens into it posteriorly. In front it leads forward between the two limbs of the mucous 

 gland, into a thin walled pouch with very long cilia (FERT.). This pouch corresponds in position 

 and in its histology to the fertilization pouch of primitive pulmonates, and forms an annexe to the 

 albumen gland where the sperms come into contact with the egg. 



The albumen gland is lined with a rather opaque white epithelium, contrasting in appearance with 

 the mucous gland. It differs from the same gland of most primitive pulmonates in still forming an 

 integral part of the duct traversed by the genital products, and bulging freely into the pallial cavity. 

 In even the most primitive pulmonates, as also in the higher opisthobranchs, the albumen gland forms 

 a diverticulum which becomes quite removed from the main channel of the genital tract, and is 

 haemocoelic in position. After copulation, the albumen gland in Limacina contains isolated sperms 

 suspended in mucoid secretion. Leading back from it, close alongside the little hermaphrodite duct, 

 runs the short tubular duct of the receptaculum seminis (REC). The receptaculum is well developed 

 only at stage 6 when it becomes tightly distended with sperm and easily recognizable in cleared 

 whole-mounted animals after staining. It forms a very spacious caecum, reaching a maximum dia- 

 meter of more than 100 /x, and it apparently increases in size suddenly after one or more acts of copula- 

 tion. It is thin-walled and lined with flattened squamous epithelium, entirely non-glandular and, so 

 far as can be made out, non-ciliated. The large masses of sperm within it are arranged in rather wavy, 

 parallel bundles, but they are never packed together in such distinct platelets as are seen in the lumen 

 of the male gonad. The duct of the receptaculum is 15-20x1 across, consisting at first of flattened 

 ciliated cells. Before its opening into the albumen gland, the duct itself becomes non-ciliated and 

 albuminiparous. The whole sac is of the nature of an outgrowth from the albumen gland. It is 

 homologous with the receptaculum of prosobranchs, and not with the bursa copulatrix, which is a 

 separate structure opening from just within the common genital aperture, and forming the sperm 

 storage sac in Aplysia (Eales, 1921) and in the majority of pulmonates. From the sketch given by 

 Hsiao, the receptaculum in Limacina bidimoides seems to correspond to what he calls the 'vesicula 

 seminalis' in retroversa, though this is a wrong name for it, since it does not store 'home' sperm 

 derived from previous male gametogenesis. This is evident by its position as a diverticulum of the 

 albumen gland, not as an outgrowth or distension of the little hermaphrodite duct as in the 'vesicula ' 

 of pulmonates or prosobranchs. In Limacina the whole of the stored sperm produced by the animal 

 in its male phase evidently remains in bundles in the cavity of the ovotestis at stage 5 ; further, the 

 receptaculum does not appear until after the penis of the same individual has disappeared. Of the 

 sperm sac described by him in this position, Hsiao states that 'masses of mature spermatozoa can be 

 seen inside this organ in the case of the mature Limacina '. His account of the origin of these sperma- 

 tozoa whether from the gonad of the same animal or from a partner at copulation is non-committal. 

 Of the ' receptaculum seminis ' described as such by Hsiao in retroversa, I can find no representative 

 in bidimoides. Hsiao states that this sac is connected with the ' basal portion of the outgoing duct ' and 

 that it consists of two portions, the first thick-walled and much folded, containing sperms normal in 

 structure and staining deeply with iron haematoxylin. The second is described as thinner walled and 

 baggy in appearance; the sperms stain only very lightly and undergo degeneration. From the position 

 of this diverticulum in Hsiao's figure and from the occurrence of sperm disintegration, it would appear 

 to correspond to a true bursa copulatrix. 



