140 TRANSACTIONS LIVERPOOL BIOLOCTTrAL SOriETY. 



strands traverse the rays (rhs), while the latter gives origin 

 to similar strands which are distributed to the genital 

 glands (^5). There are also two strands which pass from 

 the central plexus to the pyloric portion of the gut (ghs). 

 On the aboral face of the disc, between the origins of two 

 of the rays, is a rounded or pentagonal, more or less convex 

 plate, the madreporite (PL XXXVIII, fig. 2, m). Its 

 surface is traversed by meandering grooves, radiating from 

 the centre. Numerous perforations through its substance 

 (PI. XXXVI, figs. 1 and 2 ; PI. XXXIX, fig. 1, mp) con- 

 duct the surrounding water into a tubular canal, supported 

 by ring-like ossicles lodged within its walls, the water- 

 tube or stone-canal (PL XXXVIII, fig. 2; PL XXXIX, 

 fig. 1, tot). 



Passing downwards towards the oral aspect, the water- 

 tube opens into a pentagonal vessel which surrounds the 

 mouth, the circum-oral water vessel. (PL XXXVIII, figs. 

 1 and 2; PL XXXIX, fig. 1, cotvv). In Astropecteii and 

 Luidia five pairs of glandular caeca, the "brown bodies" 

 of Tiedemann {hh) are seated, interradially, upon the 

 inner border of the circum-oral water vessel, and commu- 

 nicate with its cavity. In Aster las and Solaster one of 

 these bodies is absent from the madreporic interradius. 

 The circum-oral water vessel has also communicating 

 with it a number of sacs with muscular walls, the Polian 

 vesicles (PL XXXVIII, fig. l,pv). These open upon its 

 outer border, immediately opposite the brown bodies, and 

 are, therefore, interradial. In Astropecten and Solaster 

 the Polian vesicles are large and pear shaped, while those 

 of Asterias are small and inconspicuous. From the 

 circum-oral water vessel, vessels corresponding in number 

 with that of the rays radiate (PL XXXVIII, figs. 1 and 2, 

 r2V2)) and traversing the oral aspect of its ray, inunediately 

 external to the conjoined inner ends of the ambulacra! 



