MONOGRAPH OF THE EXISTING CRINOIDS. 343 



be scattered singly in individual plates, or they may be grouped, several to a single 

 plate. 



Carpenter has noticed that in the ComasteridiB the calyx pores are generally 

 situated in the immediate neighborhood of the ambulacra, and the greater part 

 of the disk which is occupied by the large anal interradius is almost entirely free 

 from them. They are not necessarily limited to the disk, for they may also be 

 found on the lower parts of the arms and also on the proximal pinnules. In 

 both cases they open near the genital canal. In a few cases Carpenter found calyx 

 pores on the middle and later pinnules of the arms ; these open into the genital canal 

 of the pinnule, according to Carpenter, close to the point where it arises from 

 that of the arm. 



The calyx pores are the external openings of minute canals which are lined 

 with columnar epithelium, and exjiand almost immediately into ampulla-like en- 

 largements, which traverse the body wall as wider canals of uniform width, lead- 

 ing into the outer chambers of the restricted body cavity. The epithelial lining is 

 composed of closely crowded ciliated cells which have deeply stained oval nuclei. 

 These cells are 0.01 mm. high, and bear cilia 0.02 mm. in length, which in Antedon 

 mediterranea entirely fill the lumen of the ampulla-like swelling, the latter being 

 0.06 mm. in diameter. In life the cilia beat inwardly, according to W. B. Car- 

 penter. At the inner end of the calyx pores the ciliated epitheliiun passes gradually 

 over into a low flat pavement epitheliiim, which again transforms into the epi- 

 thelium lining the body cavity. On the oral side of the disk the inner end of the 

 canal often bends at an obtuse angle, so that the canal does not traverse the body 

 wall perpendicularly. There are no calyx pores on the arms beyond the second 

 brachial. On the arms the pore canals open into the genital canal or into the 

 cavities around it and in communication with it, which are extensions of the 

 body cavity. 



The radial vessels of the water-vascular system, which underlie the ambulacral 

 grooves of the disk in the comatulids, arise from the angles of the pentagonal dorso- 

 ventrally flattened water-vascular ring as single trunks situated beneath the median 

 line of the ambulacra. In addition to these five main radial branches the circum- 

 oral water- vascular ring gives off small branches to the oral tentacles. 



In Isomnus deconus and in Endoxom^niis wyvUIefhomaoni. there is a radial 

 extension of the labial plexus of the blood-vascidar system in this position, and the 

 two tnmks which ultimately unite to form the single water vessel of the ambulacriun 

 are thus kept separate for a considerable distance, 1.5 mm. or more, from the edge 

 of the peristome; that is to say, the circumoral water- vascular ring is markedly 

 stellate, instead of simply pentagonal, as in the comatulids. 



Neither the oral ring nor the radial water vessels have any ampullae connected 

 with them, though, as suggested by Ludwig, these are perhaps represented by the 

 small lateral pouches of the radial vessels which are opposite the tentacular 

 branches and are crossed by muscle threads, while the function of the ampullae may 

 be also in part performed by the muscle threads which cross the lumen of the water 

 tubes everywhere. 



142140— 21— Bull. 82 24 



