568 



THE INVERTEBRATA 



-mad. 



rm,' 



aun- 



la. 



tth^ 



Fig. 426. Aristotle's lantern of Echinus esculentus. From Shipley and Mac- 

 Bride, amp. ampullae of tube feet; arc. arch of jaw; aur. auricula; comp. 

 compass; g.sto. genital stolon; ia. interambulacral plates of shell; j. jaw; 

 m. protractor muscle of jaw; w/ retractor of jaw; m." elevator of compass; 

 m.'" depressors of compasses ; 7nad. madreporite ; oe. oesophagus ; rm. rectum ; 

 stc. stone canal; T.hd. Tiedemann's body ("Polian vesicle"); tth. tooth; 

 tth.' soft upper end of tooth; v.h.v. "ventral blood vessel"; w.v.r. water 

 vascular ring. 



