24 



funnel gradually narrows (fig. 22), then widens again 

 to form a median dilatation. Here the columnar cells of 

 the epithelium with which the funnel is lined bear long 

 cilia which, in sections, are invariably directed towards 

 the body caYitj. Beyond the dilatation the cells lose their 

 cilia and gradually thin out, until, as the lumen of the 

 funnel gradually narrows, they are replaced by those of 

 the coelomic endothelium. Occasionally two adjacent 

 funnels unite before opening into the body cavity. 



The water-vascular system of Antedon and its allies 

 differs functionally from that of the great majority of 

 Echinoderma in having no locomotor role. The function 

 of the delicate tentacles which fringe the ambulacral 

 grooves is probably respiratory ; and, as will be seen later 

 on, in the description of the nervous system, they are 

 highly sensory. The ciliated funnels and water-tubes 

 probably discharge the same function as the madreporites 

 and water-tubes (stone canals) of the majority of other 

 Echinoderma; but while, in the Echinoidea, Ophiuroidea, 

 and Asteroidea the surrounding water passes directly 

 through the madreporite and water-tube into the water 

 vessels, in Antedoji it must first enter the body-cavity 

 before passing through the numerous water-tubes into the 

 circum-oral water vessel. 



The Nervous Systems. 



There are apparently three well-marked nervous 

 systems in Ayitedon, known respectively as the Superficial 

 Oral, the Deeper Oral, and the Apical or Aboral. The 

 first of these consists of a nerve ring encircling the oral 

 aperture (PI. lY., fig. 47; PL V., fig. 52, c.o.nv.r.) in close 

 proximity to the circum-oral water vessel, and radial 

 nerves (PI. III. fig. 29 ; PI. lY., fig. 41 ; PI. Y., fig. 52, 

 arnb. nv.) which radiate from the rina: and traverse the 



