228 



TEXTBOOK OP ZOOLOGY 



ranged with the flat sides together, like cards in a filing ease. The 

 two middle rows of ossicles are called amhulacral plates. Amhulacral 

 pores, through which the tube feet project, are located between these 

 plates. The outer rows of plates, forming the margin of the groove, 





Fig. 123. — Dissection of the starfish, Asterias. The aboral wall has been re- 

 moved from the trivium and a portion of the central disc. One ray of the biviuni 

 has been turned to expose the oral surface and tube feet. The organs have been 

 removed from one ray of the trivium to expose the skeleton. Am., ambulacra! 

 groove; C.S., cardiac stomach; D.B., dermal branchiae; E, eyespot ; Cr, gonads; M, 

 madreporite ; Os., ossicle; P, pelicellariae ; P.C., ploric caeca; Py., pyloric sac; ic, 

 rectal gland ; T.F., tube feet : T.F.2, arrangement of tube feet in skeletal ray. 

 (From White, General Biology, published by The C. V. Mosby Company.) 



