78 MR. P. H. CARPEXTER OX THE GEXES ACTIXOMETRA. 



radials (figs. 4, 12 a, 17). These are not simply plane, but are usually more or less 

 divided up by delicate calcareous processes which extend to meet the ventral face of the 

 rosette, and collectively form a complicated network (c.n), filling up the central funnel, 

 and often partially bridging over the ventral radial furrow, so as to convert it into an 

 incomplete canal. 



At the inner margin of the ventral face this furrow turns downwards, and passes 

 directly into a nearly vertical furrow occupying the median line of the proximal or 

 internal face (PL IV. fig. 12 c, a.r.f), and more or less completely converted into a canal 

 by the union of irregular processes, which extend themselves from its sides to meet the 

 rosette. As it descends towards the dorsal face and passes between the inner raised edges 

 of the two apertures {/, y) of the central canal, this axial radial farrow becomes a complete 

 canal, for its edges are closely applied to the inflected margins of. one of the five radial 

 spout-like processes of the rosette (PI. IV. figs. 13, 16, p). 



The five canals thus formed may hence be regarded as enclosing cavities directly con- 

 tinuous with the cceliac canals of the arms, in the direction of which they lie ; and they 

 thus enclose portions of the body-cavity, which I will call the radial ccelom 1 . 



They open on the dorsal surface of the radial pentagon by five large openings (PI. IV. 

 fig. 16, Q), that correspond with five more or less distinctly marked circular depressions, 

 which are placed radially on the ventral surface of the centrodorsal piece around the 

 margins of its central cavity (fig. 15, q), and the cauals end blindly in these depressions. 

 "Where these canals are enclosed by the spout -like processes of the rosette, they are com- 

 pletely shut off both from one another and from the dorsal extension of the ccelom which 

 occupies the central funnel-shaped space within the radial pentagon (figs. 1, 17, F), and 

 passes down into the cavity of the centrodorsal piece through the central opening of the 

 rosette (fig. 16, r.o). On the ventral side of the rosette, however, these radial axial canals 

 are only partially complete, and are in free communication with the numerous plexiform 

 spaces into which the funnel-shaped space is broken up by the above-mentioned cal- 

 careous network. The central portion of this system is very irregular; but peripherally 

 the plexus becomes more regular, and five axial interradial canals are traceable between 

 the five radial ones, with which, as with the centre of the plexus, they are in free 

 communication. 



These interradial canals are continuous with the interradial furrows which are visible 

 on the ventral aspect of the radial pentagon (PL IV. figs. 4, 17, i'-i-f), and they enclose 

 diverticula of the circumvisceral ccelom to which the name interradial ccelom may be 

 given. They do not descend so far towards the dorsal surface as the axial radial canals, 

 and are not, like the latter, enclosed (normally, at any rate) by spout-like processes of 

 the rosette ; for their course towards the dorsal surface is terminated by the five short 

 triangular processes of the rosette (figs. 3, 7, 13, 16, o), which are directed towards the 

 sutures between the five radials. 



(§ 53) This is well seen in Ludwig's schematic vertical section through the body of 

 Ant. rosacea-, in which the radial ccelom (Lr) is rightly represented as both longer and 



1 The general relation of these axial radial canals is precisely the same in Act inometra as in Antedon. See PI. VIII. 

 figs. 3, 6, a.r.c. 2 Beitrage &c. Taf. xix. fig. 74. 



