86 LABORATORY DIRECTIONS 



(f) The mantle muscle is attached along the pallial line. 



2. Note the right and left mantle lobes and their relation 

 to one another. 



3. Note the inhalent and exhalent apertures and the margins 

 of the mantle in this region. 



4. Fold back the left mantle lobe and distinguish the two 

 gills just beneath the mantle; the foot, a heavy muscular struc- 

 ture ; the visceral mass, the enlarged region dorsal to the foot ; 

 the labial palpi two small triangular flaps at the anterior end of 

 the body. 



5. Make an outline drawing of the left side, with the shell 

 and mantle removed, to show the relation of parts. Label all 

 parts. 



6. Pass a probe into the exhalent aperture and note the 

 cavity, the cloaca, which lies above the bases of gills and pos- 

 terior to the posterior adductor muscles. Above the muscles is the 

 anal opening of the intestine. The portion of the intestine leading 

 to the anus is the rectum. 



7. Insert a probe into the mouth, which lies between the 

 anterior adductor muscle and the anterior edge of the foot. De- 

 termine the relation of outer and inner pair of palpi to the mouth. 



8. Determine the relation of the two pairs of glils to one 

 another. The gills may be distended with eggs and larvae in some 

 specimens. Locate the supra-brancial chamber and determine 

 its relation to the exhalent aperture. 



III. EXAMINATION OF CROSS SECTIONS 



1. Cut a section, about J4 inch thick, obliquely through the 

 anterior part of the pericardial cavity and the foot. Distinguish 

 the mantle, gills, visceral mass, intestine, foot, rectum and its 

 typhlosole, and ureter. Draw and label all the parts. 



2. Make a similar section through the region of the posterior 

 adductor. Determine the relation of the suprabranchial chamber. 

 Draw. ' 



