HOLOTHUROIDEA. 



255 



the cutis and circular muscles (Elasipodidae). There is appar- 

 ently no representative of the axial organ. 



v-.u. 



.VTU 



^f-'^^-^r 



fn \ \nOEoi 



I l ' ~J 



^V</vi t/i. I C//1.TUX 



FIG. 180. Diagram of a transverse section through the body-wall of a Holothurian in the 

 region of a radius (after Delage and Herouard). ejt. dermis ; cn.pd cavity of tube-foot ; 

 cn.rd radial water-vascular vessel ; cv.ep epineural cavity ; lac.p lacuna in the skin ; 

 lac.rd radial vascular strand ; mcl.c circular muscles ; mcl.cn muscles of the radial 

 water vessel ; mcl.l longitudinal muscle of the radius ; mcl.pd muscles of tube-foot ; 

 nh nerve cord of deep oral system ; n.pd pedal nerve ; rb.n radial nerve of ectoneural 

 system ; sin.rd radial perihaemal canal ; sq, s? 1 , sq.e, sq.p skeletal pieces of the dermis ; 

 sq.vnt skeletal piece of the sucker of a foot ; ves.pd ampulla ; vlv valve ; vnt sucker. 



The central nervous system presents two parts only, the 

 ectoneural ventral system and the deep oral system. There is 

 apparently no apical system. 



The ventral system consists of a circumoral ring and five 



