10 THE VOYAGE OF H.M.S. CHALLENGER. 



Behind the gill and the kidney, on the anterior edge of the liver, and partly resting 

 on the intestine, lies the foliated gland (" Feuillets muqueux," Cuv. ; " Schleimdnise " of 

 some authors). It exhibits the usual structure, and seems to open into the branchial cavity 

 by the same aperture as the kidney. 



Most of the Marseniadas are, like the other Prosobranchiata, dioecious, unisexual. The 

 reproductive gland, testis or ovary, forms the termination and the posterior portion of the 

 last twist of the superior visceral mass. They are both composed of long attenuated follicles. 



The vas deferens forms a large coiled knot, with which the windings of a tubular, 

 appendicular, prostate organ are associated. It is continued from the superior visceral 

 mass to the right wall of the inferior body-cavity, within which it extends with many 

 twistings to the penis, through which it is further prolonged to an opening at the 

 tip. Less frequently (Marsenia, Marseniella) the vas deferens passes, at the root of the 

 penis, from the body-wall into the body-cavity, where it becomes more strongly developed, 

 and extends with multitudinous coils over the foliated stomach and the bulbus pharyugeus, 

 finally entering the penis. The terminal portion of the vas deferens is, in most of the 

 genera, free within its cavity, and can be protruded, like a finger, from the apical aperture, 

 or on the other hand altogether retracted. The penis is, as we have mentioned, slightly 

 different in the various genera. — The oviduct passes from the ovary into a large mucus 

 and albumen gland, lying on the inside of the fasciculus of the right shell-muscle. Thence 

 it is continued forwards as a comparatively short, but yet strongly developed vagina, 

 which opens below the anal papilla. Just above the vulva, a special, short, strong-walled 

 diverticulum is formed by the vagina. A number of minute seminal receptacles opeu into 

 the posterior end of the mucus and albumen gland. 



Among the Marseniadse, however, several monoecious, bisexual genera occur (Mar- 

 senina, Onchidiopsis), a sexual relation not occurring elsewhere among Prosobranchiates, 

 except in the but little known genus Valvata. 1 The hermaphrodite gland exhibits the 

 usual structure ; the hermaphrodite ducts are associated with a very peculiar accessory 

 hermaphrodite gland; the common duct passing from the latter divides in the usual 

 fashion. The male duct — the vas deferens — is associated with a tubular prostate rolled 

 up into an irregular knot, and usually enveloping the greater part of the vas deferens. 

 The duct is continued onwards, in the usual way, within the body-wall to the penis. The 

 female portion forms a vaginal duct associated with an immense seminal receptacle, with a 

 thick- walled vestibular sack, and with the large two-chambered mucus and albumen gland. 

 The vagina opens by a small slit-like vulva below and behind the anal papilla. The above 

 account is based on an investigation of the monoecious apparatus of the Onchidiopsides. 



But little is yet known of the ontogeny of this group. In regard to the Marsenia? 

 proper [Marsenia perspicua) the reports of Peach, Hennedy, and Giard enable us to 



1 Moquin Tandem, Observ. sur l'appareil genital des Valvees (Mem. de VAcad. se. Inscript. et Belles-Lettr. 

 de Toulouse, ser. 4, 1852, vol. xi. p. 63); Journ. de conch., 1852, vol. iii. pp. 244-248, pi. ix. figs. 3, 4. 



