PHYLUM ECHINODERMATA 



J 93 



perivisceral part of the coelom (Fig. 133, 19) surrounds the ali- 

 mentary canal and extends into the arms. It is lined with 

 peritoneum (Fig. 133, 4) and filled with sea-water containing 

 some albuminous matter. Oxygen is taken into the coelomic 

 fluid and carbon dioxide given off through outpushings of the 

 body-wall known as papulce or dermal branchial (Fig. 133, 5). 

 The ccelom also has an ex- 

 cretory junction, since cells 

 from the peritoneum are 

 budded off into the ccelomic 

 fluid, where they move about 

 as amcebocytes gathering 

 waste matters. These cells 

 make their way into the der- 

 mal branchiae, through the 

 walls of which they pass to 

 the outside, where they dis- 

 integrate. 



The Water-vascular Sys- 

 tem. — The water- vascular 

 system (Fig. 134) is a divi- 

 sion of the ccelom peculiar to 

 echinoderms. Beginning with 

 the madreporite (m) the fol- 

 lowing Structures are enCOUn- a starfish. a, ampullae ; ap, Polian 



tered- the Stone-canal (m f ) vesides : ^, circular canal; m, madre- 

 lerea.. tne Sione canal \m ) pori te; ^madreporic canal;*, tube-feet; 



running downwards enters r, radial canals ; r', branches to am- 

 .1 • 7 / \ 1 • 1 pullae. (From Parker and Haswell, after 



the ring-canal (c), winch 5 egenbaur .) 

 encircles the mouth ; from 



this canal five radial canals (Fig. 134, r; Fig. 133, 13), one in 

 each arm, pass outward just above the ambulacral grooves. The 

 radial canals give off side branches from which arise the tube-feet 

 (Fig. 134, /; Fig. 133, if) and ampullar (Fig. 134, a; Fig. 133, 16.) 

 The ampullae are bulb-like sacs extending into the ccelom; they 

 J are connected directly with the tube-feet, which pass through *iny 



