4, ANIMAL FORMS 
mouth by means of the cilia on the great triangular lips or 
palps which bound it on each side (Fig. 45, A, p). 
ee 
Fic. 45.—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; 0, opening of reproductive kidney ; ¢, brain; ft., 
foot; g, gill; 2, heart ; i, intestine ; &, kidney ; 2, liver; m, mantle (upper fig.), 
mouth (lower fig.); p, palp (upper fig.), foot nerves (lower fig.) ; p.a., hinder 
muscle for closing the shell; s, 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. 
