AMBULACEAL APPENDAGES. ALIMENTARY CANAL. 



275 



Sc 



all cases serve for locomotion. In addition to the ambulacra! feet, 

 great tentacle-like tubes may be present as appendages of the water- 

 vascular system ; the circle of tentacles round the mouth of Ifolo- 

 thurians (fig. 209) is composed of such appendages. We also find 

 leaf-like appendages 

 arranged over four 

 or five-leaved rosette- 

 shaped areas, forming 

 the ambulacra! gills of 

 the Spatanyidea and 

 Clypeastridea (figs. 

 207 and 208). The 

 irregular Sea-urchins 

 all possess in addition 

 ambulacra! feet upon 

 the ventral surface. 

 These are in the Cly- 

 peastridea almost mi- 

 croscopic in size ; they 

 are very numerous, 

 and are arranged in 

 branched rows or are 

 irregularly distributed 

 over the surface. 



The Echinodermata 

 possess an alimentary 

 canal distinct from 

 the body cavity ; it 

 can be divided into 

 three parts oesopha- 

 gus, stomach, and 

 rectum. The anus is 

 placed usually at the 

 centre of the apical 



nolp nvplvin in intpr Fl<5 ' 21f) '~ HoMJtur - a tululita, opened long! vuTinally (after 

 6 ' Fl M. Edwards). O, Mouth in the midst of the tentacles 



Cl 



radius on the ventral 



.side. The intestine 



may, however, end 



blindly, as for example" 



in all the Ophiuridce and Euryalidce, also in the genera A&tero- 



pecten, Ctenodiscus, and Luidia, which have no anus. The mouth 



(T) D, digestive canal ; Sc, stone canal ; P, Po'iau 

 vesicle ; Eg, circular vessel of the water-vascular system ; 

 Ov, ovaries; Ag, ambulacral vessel; M, 'ongitudinal 

 muscles ; Gf, vessel tr the intestine ; CI, cloaca ; W I, 

 respiratory trees. 



