PHYSIOLOGICAL SERIES. 



.. H . ... Tli.- whole wntral ijitem, \\-hether it is 



, . . ... .. ;., leotn] body-epithelium (Asteroidea) or is 



comparatively deep-seated, always retains strong indications 

 .f ii.H epithelial origin. Two kinds of nuclei lie in the super- 

 ficial parts of the nerve-cordssome large and with distinct 

 nurlcoli, Monging apparently to ganglion-cells, others small 

 . . . N ,- iniiig, Ihe latter belong to attenuated supporting 

 epithelial 'celU that traverse the cord at right angles to its surface. 

 The spaces between them an- filled by nerve-fibrilloe. 



G C. 



N.F. 

 S.C. 



C.L. 

 stetion through the Radial Cord of Echinus esculentu*. X 700. 



(XL. Cwcctive-tiue lamina. G.C. Nuclei of ganglion (P) cells. 

 S.C. Supporting cella. N.F. Nerve-fibrils. 



of the several radial cords of the oral system from 

 the ctrcamoral ring destroys all power of co-ordinated action 

 tho different arms or segments, although the move- 

 indmdual part- of each are .-till in perfect harmony 

 themselves. From this fact the circumoral ring might 

 h* thought to he a co-ordinating c.-ntrefor the general body 

 f I : I h it higher functional value than 



the radial cord*, hut it i- probably n.-an-r the truth to consider 

 all parta of the system of equal value and the circumoral rin^ 

 imply as the path along which stimuli may pass from one 

 segment to another. 



OPHIUROIDEA. 



D. 1. Two ,pocimon.H of the oral central nervous system of a 

 Snake-armed Starfish (Ophiocoma echinatd). 



The superficial oral system consists of a pentagonal 

 ring that *urrounds the mouth near its passage into the 



