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MORPHOLOGY OF INVERTEBRATE TYPES 



spines. One plate is situated in the centre of the disc and is 

 called the central plate. It is surrounded by five radial plates. 

 To the outside of the radial plates are ten radiating rows of 



n.rd. 



cil. 



FIG. 36. Transverse section of an arm of a brittle star after Delage 

 and Herouard. c. epn, epineural cavity; ;:. /;, hyponeural oral ring; sin. rd, 

 radial sinus; en. rd, radial canal; n. rd, epineural radial nerve; n. mcl, nerves 

 of intervertebral muscles; mcl, intervertebral muscles; n. pgt, spine nerve; 

 n. cut, cutaneous nerve; c. g. I, lateral portions of the general cavity; cil, 

 ciliated groove or band of the cavity; c. g. a, axial cavity of the arm. 



interradial and secondary radial plates [usually three of the 

 former for each interradius and two of the latter for each radius. 

 At the base of each arm are basal plates (adradial), usually one 

 on each side of the distal secondary radial plate.] On the oral 



