214 ECHINODERMATA 



2. Place the starfish on its aboral surface and analyze the 

 method of righting. 



3. Tear the starfish quickly from the substratum upon 

 which it is crawling. Are any of the feet torn from the 

 animal? (See Paine 1 for a study of the adhesive power of 

 the tube feet.) 



4. Find the threadlike dermal branchiae projecting 

 through the body integument on the aboral surface. They 

 serve as respiratory organs and probably also have an excre- 

 tory function. The phagocytic nature of the cells of the 

 coelomic fluid may be studied by simple methods reported by 

 Kindred. (See reference below.) 



5. Stroke the starfish with a camel's-hair brush and notice 

 how the hairs are caught. Can you determine by what and 

 how they are held? With a hand lens examine around the 

 bases of the spines, and see the arrangement of the pedicel- 

 lariae. Their function is obscure, but they enable the star- 

 fish to hold small objects firmly and they may be of service 

 in dealing with possible surface parasites. 



6. Remove some of the pedicellariae with a scalpel and ex- 

 amine them under the microscope. Do you find more than 

 one kind? 



Draw a pedicellaria. 



Internal Structure. — Make the dissection under water, and 

 in cutting through the integument be careful not to injure the 

 underlying soft parts. 



With strong scissors cut through the aboral body wall near 

 the tips of the rays of the trivium. Carry the cuts forward 

 along the sides of the rays to the disk. The cavity thus 

 opened is the coelom or body cavity. 



Lift up the integument at the tip of each arm and carefully 

 snip away the mesenteries which attach the organs to it. Cut 

 the membranes that extend into the disk opposite the junc- 

 tions of the arms, and, cutting as close as possible to the 



1 Paine, V. L.: Adhesions of the Tube-feet in Starfish. Jour. Exp. 

 Zool., vol. 46, No. 2, 1926. 



