MOLLUSKS 



91 



mouth by means of the cilia on the great triangular lips 01 

 palps which bound it on each side (Fig. 51, A, p}. 



Ji 



a.a. 



FIG. 51. Anatomy of fresh-water clam. A, right valve of shell removed , B, dissec- 

 tion to show internal organs, a, external opening of kidney ; a.a., the anterior 

 muscle for closing the shell ; J, opening of reproductive kidney ; c, brai a ; ft., 

 foot ; g, gill ; h, heart ; i, intestine ; k, kidney ; I, liver ; m, mantle (upper fig.), 

 mouth (lower fig.) ; p, palp (upper fig.), foot nerves (lower fig.) ; p.a., hinder 

 muscle for closing the shell ; , space through which the water passes on 

 leaving the body ; st, stomach ; v, nerves supplying viscera. 



Between the halves of the shell in the hinge region is a 

 horny pad that acts like a spring, and without any muscu- 

 lar effort on the part of the clam keeps the shells open. 



