MANTLE-CAVITY. 



115 



II. DISSECTION Oi- THE MANTLE-CAVITY AND ORGANS 

 IN RELATION WITH IT. 



The respiratory or mantle cavity of the snail lies along 

 the dorsal surface, commencing at the collar, and extending 

 backwards rather more than three-fourths of the way round 

 the first turn of the spiral. The mantle is a transverse fold 

 of skin which, arising from the dorsal surface of the visceral 



Fig. 29. — Helix pomatla. Dissection from the right side to show the 

 mantle-cavity and organs in relation with it. The arrow passes 

 through the pulmonary aperture into the mantle-cavity. The shell 

 and the upper part of the spiral visceral mass have been removed. 

 (a. m. m.) 



A, auricle. B, anus, C, collar. D, dorsal body-wall forming the floor of 

 the mantle-cavity. E, eye. F, foot. G-, genital aperture. H. groove leading 

 to genital apertute. K, kidney. L, lip. P, pulmonary vein. PA, pulmonary 

 aperture. PC. pulmonary or mantle cavity. PV, pulmonary vessels in roof 

 of mantle-cavity. PV, cut ends of pulmonar.v vessels. R, nctum. S, 

 anterior tentacle. T, posterior tentacle. XT, ureter. V, ventricle, 



mass, grows forwards along the back, ending in front in a 

 thickened rim, the collar. Between the mantle-fold and the 

 back of the animal is the large mantle- cavity, which at first 

 opens anteriorly by a wide orifice. Fusion of the collar with 



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