LABORATORY WORK, XIII 357 



2. Hold the clam just below the surface of the water and by means 

 of a pipette place some carmine suspended in water near the poste- 

 rior end. Notice the results. How are they to be interpreted ? 



3. Offer carmine in sugar solution; in acetic acid; in sulphuric 

 acid. Is there any difference in the results ? 



TOPICS FOR FURTHER STUDY 



1. Habitat and food of Anodonta (or Unio). 2. Geographical dis- 

 tribution of fresh-water clams. 3. General development. 4. Allied 

 animals from fresh water, such as the Unionidse and Cycladidse ; and 

 from the sea, such as the Myidae, Veneridse, Arcidse, Aviculidse, Pecti- 

 nidae, and Ostreidae. 



XIII. STARFISH (Asterias vulgaris) 



Starfishes can be readily got at low tide in rock pools and on piles 

 and walls at the sea-shore. They may be transported alive consider- 

 able distances, if packed in wet eel-grass or seaweed. The living 

 animals may be placed for study in a soup-plate full of sea-water, or 

 water containing about 2.5 % sea salt. Dry preparations, for the study 

 of the hard parts, may be made as follows : Leave a living starfish in 

 a shallow dish of warm, fresh water until fully expanded. Next dip 

 it into boiling water until hardened, and then dry it in the sun or in 

 a slow oven. 



DRAWINGS 



(Nos. 1, 2, 4, and 5 from dried specimen, No. 3 from an alcoholic one.) 



1. Aboral view. Natural size. 



2. Oral surface of arm showing ambulacral groove. Natural size. 



3. Cross-section of arm with ambulacral feet, x 4. 



4. Ambulacral ossicles, dissected out. x 2. 



5. Spines from aboral surface, x 10. 



OBSERVATIONS ON THE LIVING ANIMAL 



Each student should be provided with a soup-plate full of salt water. 



1. Observe the eyes, the ambulacral feet and their sucking disks, 

 the gills upon the back. Has the starfish strict radial symmetry? 



2. Note the method of locomotion by ambulacral feet. With the 

 aid of a diagram show what takes place in a single foot. 



