Common Starfish. 227 



water-vascular ring-, between it and the commissural ring*, 

 or rather commissural pentagon, formed by the nervous 

 bands connecting the proximal ends of the gangliated radial 

 cords. 

 h. ' Polian vesicles ;' muscular sacculi appended to the water- vas- 

 cular circum-oral ring. There are in this species ten Polian 

 vesicles, one corresponding to each biserial row of ampullae ; 

 their functions, however, cannot be here of the importance 

 which they may possess when of the proportions observed 

 in the Holothurians (see Description of Preparation 47). 

 Corresponding again to the Polian vesicles is to be found, 

 on the internal aspect of the water- vascular ring, a series of 

 glandular sacculi, the so-called ^racemose vesicles.'' Of these 

 there are nine in this species, one being aborted at the point 

 of insertion of the madreporic canal into the ring. 

 j I andy 2. Reproductive glands of radius III, consisting of mul- 

 tiramified coeca appended to a single efferent duct, as in 

 many but not all proctuchous Asteriae, and in Ctenodiscus 

 amongst the aproctous. The efferent duct of each gland 

 comes into relation with the corresponding interradial sep- 

 tum, and the small ova find their way into the sea-water 

 through a cribriform external opening, which may be found 

 on the corresponding side of the apex of each interradial 

 angle on the dorsal surface of the body. See Miiller and 

 Troschel, Die Asteriden, pi. xii., fig. 2, p. 133. 

 j '^. Point of attachment of efferent generative duct of right 

 generative gland of radius V to interradial septum, which 

 is formed by the prolongation inwards of the external 

 envelope containing a number of small flat ossicles. 

 k I and k 2. Ambulacral ossicles forming by their mesial abut- 

 ment the commissural ambulacral arches. There may be 

 as many as 140 ambulacral arches in each ray, but as 

 each arch is never in relation with more than a single pair 

 of ampullae, and as the ampullae in Asteracanthion form 

 two biserial rows, these rows are only half as numerous as 

 the ambulacral arches. The apposition of the ambulacral 

 arches forms inleriorly the amhulacral furrow, in the upper 

 part of which is lodged the ambulacral water- vessel, and in 

 the lower part of which, immediately beneath the integument, 

 q 2 



