32 



COMPARATIVE ANATOMY 



CHAP. 



2. Pulmonata. 



Type : Helix pomatia. The visceral dome is well developed, and 

 protrudes hernia-like from the rest of the body ; it is dextrally coiled, 



and has a corresponding shell. The 

 foot is large and long, and has a 

 flat creeping sole. The head has 

 ;two pairs of feelers, one of which 

 carries the eyes. The mantle fold 

 hangs down from the anterior side 

 of the visceral dome, and covers a 

 spacious mantle cavity (respiratory 

 or pulmonary cavity). The free 

 edge of the mantle fold unites with 

 the integument of the neck near it, 

 only leaving an aperture to the 

 right, the respiratory aperture. 

 This aperture serves for the inhala- 

 tion and exhalation of the air. 

 The anus and the unpaired nephri- 

 dial aperture lie close to the re- 

 spiratory aperture, and are thus on 

 the right side. There are no gills 

 in the mantle cavity, which con- 

 tains air. Respiration takes place 

 at the inner surface of the mantle 

 fold, in which runs a fine network 

 of vessels lying in front of the 

 heart. The foot, unlike that of 

 the Prosobranchia, has no operculum. There is a common genital 

 aperture on the neck, to the right, in front of the respiratory cavity 

 (the Pulmonata being hermaphrodite). Many Pulmonata, however, 

 differ greatly in their outer organisation from the Helix type. 



FIG. 42. Diagram of a Basommatophoran 

 Pulmonate. ul, Respiratory aperture ; rgn, vas- 

 cular network on the inner surface of the mantle. 

 The kidney is incorrectly drawn. Further letter- 

 ing as in Figs. 39 and 41. 



3. Opisthobranehia. 



The respiratory organs lie behind the heart. 



(a) Teetibranehia. The visceral dome is usually not large. It 

 may be either spirally coiled or symmetrical, and is covered by a 

 variously shaped shell. The foot is large, and usually has a flat 

 sole for creeping. The head is variously shaped, and often carries 

 tentacles or rhinophores, and unstalked eyes. The small mantle 

 fold hangs down from the right side of the visceral dome, and 

 often does not quite cover the single gill lying beneath it. The 

 anus lies behind the gill, more or less removed from it. The Teeti- 

 branehia are, like all Opisthobranehia, hermaphrodite ; the genital 



