480 THE ANIMAL KINGDOM. 



lined by a ciliated secretory epithelium, but it is generally large and its 

 epithelium non-secretory. In Non-Palliata it is a wide sac extending 

 antero-posteriorly. In this group the secreting acini may be lost, e.g. 

 Phyllirhoe, but they are as a rule branched tubes scattered along the edges 

 of the chamber, e.g. Bornella. The acini are also branched in other in- 

 stances, and often grouped into two lobes, anterior and posterior, of which 

 the former may be lost (Ptdmonata). They are either large or small ; either 

 free, e. g. Fissurella, or united by connective tissue ; and are lined by a 

 ciliated secretory epithelium, with either similar or dissimilar cells. In the 

 latter case the two kinds of cells may be found, either side by side or 

 confined to separate lobes. The differences relate to form and character 

 of the excretory products. The urinary chamber either opens direct by a 

 simple aperture, e.g. Buccinum, or by a papilla, or a long duct, e.g. some 

 Pulmonata. The opening lies within the branchial cavity, either near the 

 base of the gill, or, when a duct is present, near the anus. Its position 

 seems to be somewhat variable. 



The sexes are separate in the Streptoneura, but the Euthyneura are 

 hermaphrodite, the male and female products ripening at different times 

 (successive hermaphroditism). When a Gastropod is hermaphrodite, the 

 sperm and the ova either develope in the same follicle of the gland, e.g. 

 Pulmonata, or the sperm in a central capsule, into which open a number of 

 smaller capsules containing ova, as in many ceratonotous Non-Palliata ; 

 or finally, as in Elysia (Non-Palliata Haplomorphd), there are two separate 

 glands. The genital gland consists of simple or branched acini, and usually 

 lies in or near the liver. It is often lobed or compact in form, usually 

 single but sometimes double, e.g. hermaphrodite gland of Phyllirhoe, testis 

 of Paludina. The efferent ducts are ciliated in some cases 1 . When the 

 sexes are separate the vas deferens is usually a simple canal devoid of any 

 accessory glands, e.g. Natantia. It either opens on the left side of the 

 anus, and a ciliated furrow either leads to the base of the penis, e.g. Murex, 

 Natantia, or is continued along it, e.g. S trombus, &c. ; or it is continued 

 onwards as a canal, and opens either at the base or at the apex of the 

 penis, e.g. Buccinum. The penis, placed on the right side near the head, is 

 rarely hollow and invaginable, usually solid and muscular. Accessory 

 glands sometimes open upon it. The oviduct in the lower part of its 

 course usually dilates into a uterus, the walls of which secrete albumen, or 

 more rarely there is a specialised albumen gland, e.g. Paludina, Natantia. 



1 Professor Ray Lankester states (' Mollusca,' Encyclopaedia Brit. (ed. ix.) xvi. p. 645) that the 

 Zygobranchia retain the archaic character of the absence of special genital ducts. ' The generative 

 products escape by the larger nephridium,' i. e. the right. And Wegmann, in his monograph on 

 Haliotis, maintains the same view; (A. Z. Expt. (2), iii. 1884, p. 340). On the other hand, Haller 

 states explicitly that he has found a separate genital duct in both Fissurella and Haliotis (M. J. xi. 

 1886, p. pp. 10, 14). As to Patella, Harvey Gibson agrees in his lately published memoir with the 

 statement of Professor Lankester. The Zygobranchia have no accessory sexual glands. 



