THE STARFISH 133 



mal crawl upon sand or upon a greased surface? The changes in shape 

 of the arras are accomplished by muscle fibers in the body wall. Place 

 an animal on its aboral surface and observe the righting movements. 



(d) Place a mussel {Ahjtilus) or an oyster in the aquarium and 

 see whether the starfish gives any evidence of a chemical sense. If 

 feeding occurs, observe carefully and record what happens. 



(e) Numerous minute structures, the pincerlike pedicellariae and 

 the fingerlike papulae, occur upon the external surface (c/. Fig. 62). 

 Hold a specimen just below the surface in a shallow pan of sea water 

 and watch the pedicellariae and papulae with a handlens while you 

 touch the surface gently with the point of a needle. Brush the surface 

 gently with a camel's hair brush. Can you lift the starfish by means 



3p/net) ^^ ped/oe//or/ae 



gi/h 



pec//ce//ar/ab ' '" f^tjsc/ea 



A B 



Fig. 62. — Papulae and pedicellariae of the starfish, Asterias forreri. A, a por- 

 tion of the external surface showing spines, the papulae or gills, and retracted 

 rosettes of pedicellariae. B, portion of the surface of a starfish in which the 

 rosettes of pedicellariae are extended so that they cover the tips of the spines. 

 C, the structure of a pedicellaria ; diagrammatic. 



(From H. S. Jennings, 1907, University of California Publications in Zoology, vol. 4.) 



of the brush? Pull the brush away forcibly and examine the hairs 

 with a handlens. What do these observations indicate concerning the 

 functions of the pedicellariae? Place a few small crustaceans, such as 

 crabs, shrimps, or beach-hoppers, in a dish with a living starfish. 

 How long are these small animals held fast if caught by the pedicel- 

 lariae? Some species of starfishes capture food in this manner and 

 pass it along to the mouth by means of the pedicellariae and tube feet. 

 Asterias forbesi and A. vulgaris probably do not regularly employ this 

 method of feeding. What is the distribution of the two kinds of 

 pedicellariae on the aboral surface? What is their distribution on the 

 oral surface? Does this distribution suggest a protective function in 

 any region? The presence of pedicellariae apparently explains the clean 

 externa! surface of the starfish and the absence of ectoparasites or 



