I'llVIJ.M MoLLI'SCA '.••'> 



Anoilonla. The elasticity of the liiiine opens tlie shell. ( "lusiiin 

 the shell is effected by the action of muscles. 



Notice the line on the inner surface of the shell about a half 

 inch from the free edge of the left valve running more or less 

 parallel with it. This is the mantle line to which the mantle wa.s 

 attached. The mantle is the thin sheet of tissue enveloping the 

 body and lining the shell. 



The Body (Soft Parts). — Submerge the right valve, which still 

 contains the body of the animal, in a dissecting tray of water. 

 Note the position of the two largest muscles, the ankrior (nhhirtor, 

 in the cephalic and the posterior adductor in the caudal end of the 

 l)ody. Follow these muscles to their attachments in slight 

 depressions on the shell, termed muscle scars. The.se muscles 

 close the shell working against the elasticity of the hinge which 

 opens it. Manipulate the valves so as to demonstrate the 

 elasticity of the hinge. 



The body is enveloped or concealed within the inanllc which 

 consists of two lobes, the right and left, the posterior margins of 

 which arc thickened and somewhat modified to form the siphons 

 through which water enters into and pas.ses out of the nuintlc 

 cavity (the space between the mantle folds). 



To facilitate further study, remove the left mantle lobe by 

 carefully cutting it away with scissors, leaving about an inch of 

 the lobe in front of the siphons undisturbed, taking great care 

 neither to remove nor to destroy the labial palps, which adhere 

 closely to the mantle at its cephalic margin. This exposes the 

 mantle cavity within which is suspended the nuiscular foot. The 

 dorsal part of the foot and the mass toward the hinge line lodges 

 the viscera and is termed the visceral mass. 



On either side of the visceral mass, extending into the mantle 

 space, is a pair of thin, striated gills. Kai.>^e the foot gently and 

 observe the corresponding pair of gills on the right side. 



In the posterior part of the body the thickened margins of the 

 mantle lobes form by contact the ventral or inhalant siphon, 

 dorsad of which is the smaller exhalant siphon. With these facts 

 in mind, determine by dissection the course followed by the 

 respiratory current. 



The 7nouth is situated at the cephalic entl of the body between 

 the foot and the anterior adductor nuiscle. Identify the labial 

 palps, which are somewhat n)lled and twisted Haps associated 

 with the mouth. 



