n6 ELEMENTARY BIOLOGY. [CHAP. 



S. The mouth: each labial palp is continuous with 

 its fellow across the middle line, and between 

 the lip-like ridges thus formed, lies the wide 

 mouth-opening. 



d. The anterior and posterior adductor muscles: if 

 the reflected mantle-lobe be turned down again, 

 the oval divided ends of the adductor muscles 

 can be seen. They appear to perforate the 

 mantle. 



3. Now remove the animal completely from its shell, by 

 detaching the other mantle-lobe from the valve to 

 which it is fixed, and cutting through the attachments 

 of the adductor muscles to that valve. The thick 

 dorsal border of the animal and the continuity of 

 the mantle-lobes will now be more readily made out 

 than they could be previously (2. b. 



The heart. 



<?. On the dorsal border of the animal is a clear 

 space, where the mantle is very thin and covers- 

 in a cavity filled with fluid. This cavity is the 

 pericardium, and through its walls the heart can 

 be seen beating. 



b. Pin the Anodon out in water between two pieces 

 of loaded cork, or paraffin, so that its dorsal 

 border is upwards, a mantle-lobe spread over 

 each bit of cork, and its foot and gills hanging 

 down between the two pieces: then carefully cut 

 away the dorsal side of the pericardium without 

 injuring the heart. 



c. The heart will now be exposed; it is a yellow- 

 ish transparent sac, exhibiting regular contrac- 



