Chap, xii.] NERVOUS SYSTEM OF CRINOIDS. 



409 



the nerve in the arm of a starfish, and it has similar 



relations to a nerve ring which runs round the mouth. 



If we now look at the opposite side of the section, we 



find another and larger 



cord which gives oft 



branches to the muscles 



of the arms (a a'} ; this 



cord, if it be followed 



up, will be found to 



end in an organ, the 



so - called " chambered 



organ," which lies in 



the centred orsal piece 



(see page 292) of the 



Crinoid. Now, if the 



visceral mass, part of 



which is the circumoral 



nerve ring, be alone 



removed, the arms will 



continue to move as 



regularly as they did 



before, and the Crinoid 



will still be able to 



about in the 

 If, 011 the other 



the five - cham- 



>rgan be stimu- 



then, as Dr. 

 has shown, 

 sudden and 



swim 



water 



hand, 



bered 



lated, 



Carpenter 



there is a 



CL 



simultaneous 

 all the 



flexion of 

 arms. The ex- 



Fig. 177. Cross Section of a Pin- 

 nule of the Arctic Featber- 

 star (Antedon eschnchti] ; x 75. 



a, Axial cord ; a', its branches ; ag, ambu- 

 lacra! groove; b, radial blood- 

 vessel ; gv, genital vessel ; ov, ovary ; 

 n, radial nerve ; pj, pinnule joint ; 

 w, water-vessel ; T, tentacle. (From 

 Carpenter, altered from Ludwig.) 



istence of these two 



apparently independent nerve systems in a Crinoid 

 is a difficulty which the morphologist has not yet 

 been able to solve, but the anatomical and physio- 

 evidence in favour of the nervous nature 



logical 



