108 University Geological Survey of Kansas. 



is generally a muscular organ, hatchet-shaped in most fresh- 

 water clams ; it aids the animal in moving. Sometimes this 

 organ secretes a substance which hardens quickly on being ex- 

 posed, and by this means the animal cements its shell firmly 

 to some rock or other object. The foot generally becomes 

 small in such cases on account of disuse. There is an opening 

 in one of the valves for it, so that the attachment may be more 

 certain. This opening is called the byssal groove or notch, and 

 the foot, in this case, is called the byssus. 



There are other muscles in the clam which are important. 

 One or two large muscles are used in closing the shells together, 

 and run nearly directly across from one shell to the other, and 

 when two are present one is located near the front of the shell 

 and the other near the rear of it, and are known as the anterior 

 and posterior adductors, respectively. These muscles are firmly 

 attached to the shell, causing a depression in it, showing the 

 size, shape and position of the muscle. 



The pelecypods have no true heads. In the front part of 

 the animal is an opening, or mouth, surrounded by a pair of 

 membranous flaps. In the oyster these flaps are called the 

 beard. This opening is the end of the esophagus, or gullet, 

 which leads to the stomach, which is generally surrounded by 

 the liver. From the stomach the intestine is somewhat convo- 

 luted, generally passing through a part of the heart, and finally 

 ending near the back part of the shell. 



The circulatory system consists of a heart, having two or 

 three chambers and a few arteries. The heart propels the blood 

 from the gills through the body of the animal. The respira- 

 tory organs consist generally of two pairs of gills. The water, 

 in the siphoned clams, enters through one side of the siphon, 

 or one tube, flows over the gills, constantly bathing them with 

 fresh water, and then flows past the mouth, where the food 

 particles are selected out of it, when it passes out of the other 

 siphon tube. 



The nervous system consists of two knots of nerves near the 

 mouth and one near the posterior adductor muscle. 



Now, since we have a general idea of the anatomy of the 



