ASTERIAS FORBESI Desor 



Material. Specimens of Asterias forbesi may be collected 

 among rocks between the tides or in tide-pools. Excellent dry 

 specimens may be obtained by suddenly pouring boiling water 

 into the dish in which the starfish has been allowed to assume 

 the attitude of perfect radial symmetry. For the study of in- 

 ternal organs and especially of the ambulacral system injected 

 specimens are highly recommended. The injection may be 

 accomplished without difficulty through one of the radial canals 

 and should be continued till the ambulacral feet of all radii are 

 injected. The specimens may be then preserved in formalin. 

 Injected specimens are also for sale at most of the marine 

 laboratories. Very small specimens should be fixed for sections 

 in Perenyi's fluid for which purpose each arm is severed with a 

 sharp razor. Decalcifying before imbedding is imperative. 

 Staining in haematoxylin with counterstaining in eosin or orange 

 G is advisable. 



Descriptive Part 



Asterias forbesi is a common starfish of the Atlantic Coast. 

 Like all echinoderms it shows radial symmetry inasmuch as 

 each of its five arms contains the same set of organs. But this 

 radial symmetry is not the original plan of structure and a closer 

 examination of the starfish reveals the fact that it is built on 

 the principle of bilateral symmetry. This plan is determined 

 by the position of the so-called madreporic plate which is situated 

 on the dorsal surface of the central disc between two of the 

 arms. The plane of symmetry bisects therefore the madreporic 

 plate, the anus which is situated in the middle of the dorsal sur- 

 face of the central disc, and the arm or radius opposite to the 



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