100 ANIMAL BIOLOGY 



the valves of the shell. The clam makes use of the foot in 

 burrowing into the mud where it commonly lives with the 

 siphons exposed to the water. The water, which in pass- 

 ing through the gills subserves the function of respiration, 

 affords also the means of bringing the animal its food which 

 consists of microscopic organisms and other fine materials 

 swept in by the ciliary current. The solid bodies are 

 carried by ciliary action into the mouth which is situated 

 between two pairs of flaps called the labial palpi at the 

 anterior end of the body. The mouth leads by a short 

 tube to the stomach which receives the ducts from a large 

 greenish digestive gland commonly called the liver. The 

 stomach leads to the narrow intestine which after coiling 

 about in the body opens near the posterior end of the body 

 where its contents are carried out through the exhalent 

 siphon. 



The clam is furnished with a heart consisting of a median 

 ventricle and two lateral auricles lying in a space called 

 the pericardium in the dorsal side of the body. The intes- 

 tine passes through this pericardium and is surrounded by 5 g 

 the ventricle of the heart. The beating of the heart j 

 carries the blood through arteries to various parts of the 3 ui 

 body. On its return it goes through the gills where it '- 

 takes up oxygen and loses a part of its waste products, - 



and then passes into the auricles and thence into the 



(/) jj 



ventricle. Just below the pericardium is a pair of dark- 

 colored excretory organs or kidneys which open at one end 

 into the pericardium and, at the other, to the outside of 

 the body. 



The nervous system of the clam consists of three main 

 pairs of ganglia connected by nerve cords or commissures. 

 The cerebral or brain ganglia He over the mouth. These 

 are connected by long commissures to a pair of large vis- 

 ceral ganglia just below the posterior adductor muscle. 



