116 THE SNAIL 



(c) The heart, which may be seen from the outside through the mantle. It 

 is situated in the pericardium at the back of the mantle, on the left 

 side ; and it has two chambers, an auricle and a ventricle. The main 

 pulmonary vein leads into the auricle of the heart. 



(a) The triangular-shaped kidney lying beside the heart. 



(e) The spirally-coiled visceral region, mainly composed of the brown liver 

 or bilobed digestive gland. 



(/) The albumen gland, embedded in the liver on the right side. 



Heart 



Pulmonary veins 

 Mantle 



Kidney 



Mver Albumen gland 



Flo. 36. — The Snail (Helix). Dorsal view after removal of the shell. 



{g) The columellar muscle, along the inner side of the spiral. It is attached 

 to the columella of the shell, and it enables the snail to withdraw inside 

 the shell. 



Internal Structure. 



1. Insert the point of your scissors into the pulmonary aperture, and open 

 the pulmonary cavity by cutting round under the base of the collar towards the 

 left-hand side backwards as far as the heart, taking care not to cut through the 

 floor of the mantle-cavity. Pin the mantle over towards the right-hand side. 



Examine the mantle and note : 



{a) The heart, consisting of a thin-walled auricle and a muscular pear- 

 shaped ventricle, enclosed in the pericardium. 



{b) The pulmonary vein, branching over the mantle and leading into the 

 auricle. 



(c) The triangular-shaped kidney lying next to the heart. 



{d) The ureter, passing from the kidney and extending along and above the 

 rectum, which opens at the anus situated in the pulmonary aperture. 

 The opening of the ureter is above the anus. 



(e) The reno- pericardial canal or nephrostome, a narrow cihated passage 

 between the kidney and the pericardium. Its pericardial opening is 

 opposite the ventricle. 



2. Cut through the collar in the middle line and continue the incision back- 

 wards up the spiral and forwards to the region between the large tentacles. 



