Introduction to Animal Morphology. 295 



they may be leaf-like or like a row of threads (Patella), in a 

 collar or in a pouch (near the cavity) at the dorsal side of the 

 body whorl, bounded beneath by the body wall, above by the 

 mantle, and behind by the union of the two : on the floor of 

 this cavity is the vagina, or the seminal groove ; between this 

 and the anus is the opening of the kidney. The mantle may 

 be bi-lobed and a gill pair present (Haliotis, Vermetus, Ma- 

 gilus, Conus, Pleurotoma, &c.) In Strombus, Natica, Mo- 

 dulus, only a slight band, as long as the right gill, marks the 

 place of the left gill. This rudiment is broad in Cassis, short 

 and triangular in Cypraea, absent in Sigaretus, Pteroceras, 

 Calyptraea, Littorina, Nerita. In Janthina and Valvata the 

 long gill filaments protrude out of the mantle cavity. The 

 gill shapes usually vary with the shell shapes. In Turbo the 

 gill cavity is divided, and each gill lies in a separate space. 

 This is imperfectly the case in Phasianella. 



Passage forms from the branchiate to the pulmo- 

 nate division occur in Ampullaria, where the wall of 

 the mantle cavity at certain places shows large 

 vascular plexuses coexisting with the gills. In the 

 Neurobranchiata the same arrangement occurs, but 

 the gills become obsolete. The presence of a siphon 

 in most of these shows their affinity to Prosobranchs. 

 In the pulmonates proper this part of the mantle ca- 

 vity is shut off from the rest as an air-chamber, and 

 has a muscular wall, a narrow mouth with a circular 

 sphincter; rarely dermal gill-processes coexist, as in 

 Onchidium. Ancylus and Acroloxus have no pul- 

 monary cavity separate from the general mantle 

 cavity. The aquatic Limn;i>a uses its air rh;unl>'M- as 

 a float. 



in^l-, while or yellowish, lanu-llar 



or sj> rontainintf uric arid, and omMsiinvr 



of an inlernal part, opening into tin- pericardium, and 

 an external, opening near the* anus. 



