PLUTEUS-LARYA OF ECHINUS. 



571 



municates with a cavity in the interior of the body, which is 

 surrounded by a poison of the Yolk-mass that has returned to the 



Embryonic development of Echinus: — A, Pluteus-larva at the 

 time of the first appearance of the disk ; a, Mouth in the midst 

 of the four-pronged proboscis ; b, Stomach ; c, Echinoid disk ; 

 d, d, d, d, four arms of the Pluteus-body ; e, Calcareous frame- 

 work ; /, Ciliated lobes ; g, g, g, g, Ciliated processes of the pro- 

 boscis ; — b, Disk with the first indication of the Cirrhi : — c, Disk, 

 with the origin of the Spines between the Cirrhi: — d, more 

 advanced Disk, with the Cirrhi, g, and Spines, x, projecting con- 

 siderably from the surface. (N.B.— In Figs, b, c, and d, the 

 Pluteus is not represented, its parts having undergone no change, 

 save in becoming relatively smaller.) 



