XVIII 



ECHINUS ARISTOTLE'S LANTERN 



525 



jections of the upper wall of the lantern-coelom. These projections 



Fig. 234. Echinus, esculentus dissected in order to display Aristotle's lantern, x 2. 

 The whole upper part of the shell has been cut away. 1, Upper growing end of 

 tooth ; 2, outer forked end of one " compass ' ; 3, muscle joining adjacent compasses 

 and acting as elevator of these ossicles ; 4, depressor of the compasses ; 5, lower end 

 of jaw ; 6, retractor of the whole lantern ; 7, protractor of the whole lantern ; 8, 

 auricle; 9, ampullae of the tube - feet ; 10, interambulacral plate; 11, lower part 

 of tooth; 12, water- vascular ring; 13, meeting-point of a pair of epiphyses; 14, 

 so-called Polian vesicle, really equivalent to Tiedemann's body in an Asteroid ; 15, 

 oesophagus ; 16, so-called ventral blood-vessel ; 17, genital stolon ; 18, stone-canal ; 

 19, rectum ; 20, aboral sinus. (Partly after Chadwick.) 



are the growing points of the teeth, whose lower ends pierce the 



