ECHINOIDEA 567 



Aristotle's lantern (Figs. 425, 426), which supports the teeth. The 

 lantern consists of five com^ositQ jaws; each clasping a tooth, and five 

 radial pieces, known as rotulae, which unite the jaws aborally. The 

 teeth can be moved outwards and inwards by muscles running from the 

 jaws to radially placed arches, known as the auriculae, which arise from 

 the inside of the corona near the lantern. Under each auricula, which 



e. , aos. 

 All- / .mad. 



mad.vcs. 

 1 mad. 



Fig. 425 . A diagram of a vertical section oi Echinus, passing on the left through 

 a radius and on the right through an interradius. Certain structures not 

 immediately in the plane of section are shown. A, Whole section, B, The 

 region of the madreporite. amp. ampulla of tube foot; amp.' madreporic 

 ampulla; An. anus; aos. aboral sinus, with genital rachis; arc. arch ossicle 

 of jaw; aw. auricula; d.b.v. "dorsal blood vessel"; e. pigment spot in ocular 

 plate ; epin . epineural canal ; g.sto . genital stolon ;/. jaw (not strictly in section) ; 

 j.' lower part of the same; l.coe. lantern coelom; M. mouth; m. muscle (pro- 

 tractor) which pulls down the jaw and protrudes the tooth; w/ muscle 

 (retractor) which pulls back the jaw; ?nad. madreporite; mad.ves. madreporic 

 vesicle ; n. nerve ring , oe. oesophagus ;^er.coe. perivisceral coelom ; ra.n. radial 

 nerve; ra.wv. radial water vessel; rm. rectum; rot. rotula; sh. shell (corona); 

 sip. siphon; st. stomach; stc. stone canal; T.bd. Tiedemann's body ("Polian 

 vesicle"); tf. tube foot; tth. tooth; v.b.v. "ventral blood vessel"; zvvr. water 

 vascular ring. 



perhaps represents a pair of ambulacral ossicles, runs a radial nerve, 

 with its epineural canal, and the radial perihaemal canal, " blood vessel", 

 and water vessel. Within the lantern is a space, known as the lantern 

 coelom, which is an enlarged perihaemal ring. Muscles, running 

 from the auriculae to slender ossicles, known as compasses, which 

 overlie the rotulae, can raise and depress the roof of the lantern, and 

 thus pump the fluid of its coelom into and out of the gills. In some 

 urchins, but not in Echinus^ pouches of the lantern coelom project 



