/. ASTEROIDEA. 



■fcion, and the animal can work its way through narrow openings. 

 Of the skeletal pieces the ambulacral plates need special mention. 

 A B 



JFiG. 312.—^, croas-seotion of starfish arm (orig.). a, adambulacral plates; am, ambu- 

 lacra; ap, ambulacral plates; 6, branchiae; c, coelom: /(, hepatic cteca; /, inter- 

 arabulacral plates; 71, radial nerve; p, ampulla; r, radial canal; ?,', radial blood- 

 vessel, i/, ambulacral plates, ventral view, showing the ambulacral pores 

 between. 



These form the roofs of the ambulacral grooves, and between them 

 are openings, the ambulacral pores, through which connexion is 

 made between the ambulacra and ampulla;. In each arm the pairs 

 of ambulacral plates meet above the groove like the rafters of a 



Piri. 313.— .-Isfev/snis verrnculatus, aboral surface removed. (After Gegenbaur.l g 

 gonads; /i, hepatic ca<ca ; /, stomach with anus. 



roof. Laterally each ambulacral plate abuts against a small inter- 

 ambulacral plate, bearing usually movable spines. Beyond these 

 comes the adambulacral plates, and then tliose of tlie aboral sur- 

 face. Each ambulacral area terminates at the tip of the arm with 

 an unpaired (ocular) plate. 



