PRINCIPLES OF ANIMAL BIOLOGY 63 



la. Note the two siphonal openings with fringed borders at one end 

 of the shell. With a pipette carefully and without touching 

 the animal put some powdered carmine mixed with water 

 just opposite the openings and demonstrate that water enters 

 one (inhalent) and leaves the other (exhalent). 



16. Observe the large fleshy, plow-like foot, buried in the sand. 

 It may be seen if the animal is near the sides of the glass dish, 

 or demonstrated by lifting the animal quickly before it 

 contracts. 



Ic. Make a sketch or diagram of a mussel from the side, showing the 

 position of the long axis of the shell, that of the surface of 

 the sand, the siphonal openings (with direction of the current 

 for each shown by an arrow), and the outline of the extended 

 foot. The lower end is the head, or anterior end, the upper 

 is the posterior end. The dorsal surface is that bearing the 

 hinge with its dark brown ligament. Make a full page 

 sketch, since other structures are to be drawn in later. 

 2. Study fresh or preserved material, including some females with 

 young (glochidia) in the gills. 



2a. Remove the right valve of the shell by cutting against its inner 

 surface, with a stout knife, the strong adductor muscles, one 

 near each end, and pushing the mantle from the valve to be 

 removed. Place the half of the shell containing the animal 

 in a dissecting dish and cover with water. 



26. Note the mantle lining the other shell valve, and the mantle 

 cavity between the two lobes of the mantle. In the mantle 

 cavity find: 



2c. The gills, two leaf-like structures on each side. Turn back the 

 upper pair and find: 



2d. The hard, contracted foot near the anterior end on the ventral 

 side. It continues backward into the visceral mass which 

 contains alimentary canal, reproductive, circulatory and 

 excretory organs. These will not be dissected, but may be 

 seen in charts of typical mussels. 



2e. The labial palps, triangular ridged flaps, two on each side just 

 anterior to the gills. 



2/. The mouth opening between the labial palps of the two sides. 

 Probe it with the blunt end of a needle or other instrument. 

 Sketch in natural position the foregoing parts in the outline 

 already made. 



2g. With dissecting microscope examine the surface of a living gill 

 and note the numerous small openings leading into its in- 

 terior. With compound microscope observe the cilia which 

 cause water currents to pass in through the openings. These 



