MANTLE-CAVITY. 123 



h. The hermaphrodite gland is a small yellowish body- 

 on the inner side of the upper half on the second 

 turn of the spiral. 



i. The columellar muscle, by which the animal can be 

 retracted within the shell, runs along the right 

 or inner side of the spiral, and is attached to the 

 columella in the upper half of the first turn. 



II. DISSECTION OF 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 

 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 

 the body-wall reduces this orifice to a small round aperture 

 on the right side, the respiratory or pulmonary aperture, 

 through which air alternately enters and leaves the cavity 

 during respiration. 



In close relation with the mantle-cavity are the rectum, 

 the heart, and the kidney and ureter. 



Place the snail in a dissecting dish under water, and pin 

 it firmly down through the foot, with the dorsal surface upward. 

 Open the mantle-cavity by a transverse incision through its 

 thin roof, immediately behind the collar. Cut backwards from 

 each end of the incision along the sides of the cavity to its posterior 

 end, cutting along the left side close to the junction of the mantle 

 and body-wall, and along the right side about a quarter of an 

 inch to the left of the prominent ridge that borders this side, 

 midway between this and the right border of the kidney. 



Turn back the roof of the mantle-cavity, and pin it down 

 so as fully to expose the pericardium and kidney. 



