202 THE BIOLOGY OF THE ANIMAL 



E. — The Examination of Transverse Sections. 



Wedge open the valves of living specimens and 

 put them into one per cent, chromic acid for about 

 two days, then transfer to seventy per cent, and 

 ninety per cent, alcohol for one day each. Ee- 

 move the body from the shell, being careful to 

 disturb the parts as little as possible. Place the 

 mussel on a board, and with a razor cut the en- 

 tire body into a series of parallel transverse sec- 

 tions, about a quarter of an inch thick. Float 

 these sections in order in a long dissecting-pan 

 containing fifty per cent, alcohol, and study the 

 relation of the various organs. 

 Draw the following sections : (1) Through the stom- 

 ach, (2) through the heart, (3) through the middle of 

 the posterior adductor muscle. 



As regards structure, which of the animals that you 

 have studied does the mussel most closely resemble ? 



Habits. 



A number of interesting observations on the habits 

 of the fresh- water mussel may easily be made by placing 

 specimens in an aquarium or in tubs or pans having the 

 bottom covered with three or four inches of sand or 

 mud. By changing the water from time to time the 

 animals may be kept alive for weeks. Study the posi- 

 tion of the animal in the water, the manner in which the 

 foot is used as an organ of locomotion, watch the water 

 flowing into and out of the siphons by scattering parti- 

 cles of indigo near the orifices, test the sensibility of the 

 siphonal tentacles by gently touching them with a bris- 

 tle, etc. 



For comparative work use the clam {Mya or Venus) or 

 the oyster {Ostrea). 



