108 



MUSSK1.8, (.'LAMS, OYSTEliS, SNAILS, SliL'lDS 



slowly extended outward and dowaiward into the mud and 

 anchored there. Then the retractor mu.scles contract and 

 IJull the shell and botly up to the foot, as it were. By a 

 rejietition of these movements of the foot the nuissel covers 

 consideral)le distances in the course of time. 



The alimentary canal and digestion. — The mouth is 

 just under the anterior adductor muscle and between two 

 pairs of soft flaps, the labial palps. It leads by a short 

 gullet to the spherical stomach, which is surrounded by a 



dark green mass, the 

 Posterior adductor muscle.., di(jestive (jland, or 

 Digestive ghind^ jj^^^j.^ . u^.^^. „ ^he' in- 



JJreter: testine passes down- 

 ward from the stom- 

 ach, coils once or 

 twice in the abdo- 

 men and foot, and 

 returning, runs ])os- 

 teriorly through the 

 \'entricle of the heart 

 and ends back of the 

 The food, which con- 

 sists of minute i.)larit and animal organisms, is lirought in 

 by the inhalent current, carried to the anterior end of the 

 body (Fig. od), and directed into the niouth l)y the cilia of 

 the labial pali)s. It is acted upon I\v the liuitls from the 

 digesti\'e gland and is absorbed from tlie stomach antl 

 intestine. 



Excretory organs. — The excretory organs consist of a 

 pair of dark-colored kidneys lying just lx>lo\v the pericar- 

 dium and in front of the posterior adductor muscle (Fig. 

 r)S). ]i]ach kidney consists of a glandular portion, the 



Fin. .58. — Internal stru<;tlire of a clam. 



])osterior adductor muscle (Fig. .18). 



