A LAND SNAIL 107 



The pericardial canal is opposite the ventricle and cannot be 

 seen easily. The ureter may be easily traced. It is a wide 

 canal which leaves the kidney at its forward end near the place 

 where the pulmonary vein approaches the kidney ; it first runs 

 along the inner side of the kidney to its hinder end ; here it 

 doubles on itself and passes forward to the inner edge of the 

 mantle, where it runs beside the rectum to a point near the 

 respiratory pore and opens into the mantle cavity. 



It will be noticed that the heart and the kidneys are 

 both asymmetrical organs. The heart has but one auricle; it 

 will be remembered that in the lamellibranch the auricles 

 are paired organs ; one of the pair must thus be wanting in 

 the snail. There is also only one kidney and one ureter, 

 instead of a pair of each, as in the lamellibranch. It is the left 

 member of the pair in each case which is wanting. 



Exercise 4. Draw a view of the inner surface of the mantle on a 

 scale of 3, showing the organs mentioned above ; label all. 



The digestive system. Pass a bristle through the anus into the 

 rectum in order to mark it. With two strong pins firmly fasten 

 the extreme forward end of the animal's foot and also its hinder 

 end to the wax of the dissecting pan. With sharp, fine scissors 

 cut through the floor of the mantle cavity and the collar in the 

 median line ; carry the incision forward in the median line along 

 the head between the base of the tentacles to the mouth. Care 

 should be taken in making this incision not to cut the organs 

 beneath. Spread the flaps as widely as possible to the right 

 and left and pin them down, exposing thus the organs in the 

 forward part of the body. 



The white organs on the right side of the body belong to the 

 reproductive system. The- large dark organ in the center, or 

 on the animal's left, is the stomach. Find the slender curved 

 oesophagus which leads forward from it to the dorsal side of the 

 large muscular pharynx. The oesophagus is encircled by the 



