ECHINODERMATA 563 



spending to the muscles between the vertebrae and formed by increase 

 of the coelomic (deep oral) component of the cord. The perihaemal 



ver. 



tis^. coe. fi^j^ii^ 



v.plt. 



Fig. 420. A section through an arm of an ophiuroid. Diagrammatic, magni- 

 fied. From Shipley and MacBride. coe. coelom; d.plt. upper plate; epin. 

 epineural canal; la.plt. lateral plate; In.m. longitudinal muscle; ped.ga. pedal 

 ganglion; ram. radial nerve cord; ra.peh. radial perihaemal canal; ra.wv. 

 radial water vascular canal; sp. spine; tf. tube foot; tiss. soft tissue support- 

 ing plates; ver. "vertebra"; v.plt. under plate. 



wv.sy. 



g.TCh. 



■ '■ ecct.tr.mx 



or.plt 



Fig. 421. A diagram of a section of an ophiuroid, passing through an 

 interradius and part of the opposite arm. From Shipley and MacBride. B.zv. 

 body wall; coe. coelom; coe.' coelom of the arm; ext.ir.m. external interradial 

 muscle; g.rch. genital rachis lying in the aboral sinus; in.ir.m. internal inter- 

 radial muscle; M. mouth; M.pap. mouth papillae; n. nerve ring; n.' radial 

 nerve with epineural canal: the ganglia are not shown; or.f. ist oral foot; 

 or.plt. oral plate ; Po. Polian vesicle ; ra.peh. radial perihaemal canal ; tor. ossicle 

 known as torus angularis; tr.m. transverse muscle of the 2nd joint; wv.sy. 

 water vascular system : to the left the circumoral ring, to the right the radial 

 vessel ; i , ist ambulacral ossicle which is displaced into an interradius ; 2, 3,4, 

 2nd to 4th ambulacral ossicles or "vertebrae"; i, ii, iii, ist to 3rd under 

 (" ventral ") plates. 



vessel is shallow and not divided by a septum. The tube feet have no 

 suckers and no ampullae and are often provided with warts of sense 

 cells. 



36-2 



