220 CTENOPIIOR.E. Part II. 



points of attacliinent throughout the system. The cells which radiate from the 

 corners {Fi^/. 21 a^) of the digestive cavity and thereabouts occupy at their outer 

 ends the whole breadth of the nearest interambulacral band (A, E) of the peripheric 

 system ; while those which arise from the sides of the digestive cavity, midway 

 between its corners («') and the vertical tubes (/• r) which embrace it, terminate 

 against the four chymiferous tubes (/" P and V' f) which lie nearest to the oral 

 plane. In this as well as in the instance of the other four chjaniferous tubes, 

 nothing Ijut their thin wall separates the motory cells from the circulating fluid, 

 and therefore this sj'stem must have an innnediate and direct influence upon the 

 diameter of these channels. The four peripheric bands (B, D, F, H) which lie 

 intermediate to those in the oral and tentacidar planes receive the outward 

 prolongation of all those cells which arise at the median third of the digestive 

 cavity and close upon the vertical chymiferous tubes (r r). The four peripheric 

 chymiferous tubes (/^ P and /^ P) Avhich trend nearest to the tentacular plane 

 receive the ends of those cells which arise from the vertical tubes (;■ r) on the 

 sides which ftice toward the corners of the digestive cavity. The two peripheric 

 bands (C, G) which lie in the tentacular plane have no connection whatever Avith 

 the radial system, excepting a very small part of their terminations, which extend 

 beyond the opening [f) of the tentacular sockets and toward the abactinal area; 

 but all those cells {Fig. 21, and 23 nr) which radiate from the vertical tubes (r r) in 

 jn'oximity to the tentacular ])\im.(i terminate against the proximal side of the ten- 

 tacular apparatus {li} /r), and occupy the whole breadth of the same. The length 

 of the span of this part of the radial system varies very much, according to the 

 degree of expansion or contraction of the body ; but it usually decreases in the 

 direction of the main chymiferous tubes {c c). In the oral region this sj^stem 

 merges into the lateral sj'stem along the tentacular plane, the cells of the former 

 {Fi(/. 23 )u") having the same general trend as the latter [m^), which radiate from 

 the base (/") of the tentacular sockets to the oral area. 



It is a difiicult matter to distinguish the two systems from one another, when 

 they are seen in profile. But, l)y a study of the boundaries of the lateral system 

 from another point of view {F/(j. 21), Ave find that all those cells which radiate 

 from tlie tentacular sockets to the oral area, even close up to the terminations 

 of the vertical tubes (;• r), belong to this system ; Avhereas only those cells 

 Avhich radiate from the aforesaid vertical tubes belong to the radial system in this 

 plane. In regard to that portion of this system Avhich radiates from the axial 

 fiuniel (/ ), Ave have only to add a Avord or two, to point out, partly in reiteration 

 of Avhat has already been stated, the tact that the cells {( f) trend altogether from 

 one axial line toward the j^eriphery, and are only interrupted at two opposite points 

 by the tentacular sockets (/). 



