50 PRACTICAL ZOOLOGY. 



of the epidermis. Trace the right and left mantle 

 lobes to their points of union before and behind. 



3. Examine the thick, dark-colored, hinder edge of the 

 mantle lobes, and see how by their manner of meeting 

 they form the two short tubes, the siphons, seen in 

 the live clam ; prove the great sensitiveness of the 

 margins of these siphon tubes. Are the margins of 

 the two openings alike ? 



4. Examine the ends of the anterior and posterior ad- 

 ductor muscles where they were cut off in opening 

 the shell ; scrape away any part of these muscles that 

 may remain attached to the left valve, and note the 

 marks or muscle scars which are shown. 



5. Turn the mantle lobe back as far as it will go, and 

 observe the soft abdomen; its tough lower border is 

 the foot j prick it with the dissecting needle, and ob- 



' serve what follows. 



6. Along each side of the abdomen and extending back 

 of it are two thin membranes, the gills, showing ver- 

 tical parallel markings (sometimes the outer gill is 

 thick, and of a dark color) ; study closely the rela- 

 tions of the gills to each other, to the body, and to 

 the mantle. With a knife scrape off a little of the 

 surface of the gill and examine under the microscope 

 to see the vibratory motion of the hair-like projec- 

 tions, or cilia, borne on the cells thus obtained. 



7. In front of the gills, on each side of the body, are two 

 thin, triangular flaps, much smaller than the gills, the 

 labial palpi. 



8. Raise the hind border of the left mantle lobe, and 

 observe that the gill next to the body unites with the 

 corresponding gill of the other side, thus forming a 



